How stable is the average protein

Proteins

Proteino [from Greek prōtos = the first (substance)], Proteins, protein substances, protein bodies, which mainly consist of the 20 proteinogenic α-L-amino acids (Color plate) through Peptide bonds (Peptides) primarily linear polymers (biopolymers) which, however, due to covalent, ionic, polar and hydrophobic interactions (chemical bonds) are able to form highly specific spatial structures adapted to the respective functions. The term "protein" is historical and goes back to the original isolation from the chicken egg white (chicken egg). However, it was shown relatively early on that proteins are components of practically all living cells and that, due to their structural diversity, they play an essential part in almost all life processes (life). Therefore, today the term “protein” coined by Berzelius in 1838 (from Greek prōteios = first-rate) is generally preferred to the older term “protein”. For example, while a cell of Escherichia coli contains around 3000 different proteins, there are more than 100,000 different proteins in the human organism.
Structure and structure: The structure of the proteins from the 20 different amino acids is written, i.e. with a sequence of the individual amino acids that is characteristic of each protein, also known as Leftovers (primary structure, amino acid sequence; see below). The chain length is also characteristic of each individual protein and ranges between just a few amino acid residues (e.g. 21 in the A chain of insulin; hormones) and over 1000 amino acid residues, which corresponds to relative molecular weights of 2000 to over 100,000 (macromolecular chemical compounds). All peptide bonds of a protein contain the same sense of direction as they are derived from the “head-to-tail connection” of the individual amino acids. This ultimately also results from the Amino terminus and the Carboxyl terminus Defined polarity of each protein chain (as agreed, the amino terminus is always written at the beginning, the carboxyl terminus at the end of an amino acid sequence). Because the individual amino acids are linked by peptide bonds, a protein chain consists of regularly repeating units, the so-called. backbone, and the various Side chains of the individual amino acids. The pure proteins contain the chemical elements (bio-elements) C (carbon), H (hydrogen), O (oxygen), N (nitrogen) (contained in every amino acid residue) and S (sulfur; only in cysteine ​​and Contain methionine). In addition to these 20 proteinogenic amino acids, certain proteins also contain modified amino acids (e.g. N-formyl methionine at the amino terminus of bacterial proteins, hydroxyproline and hydroxylysine in collagen), metals, in mostly small proportions(Metalloproteins), prosthetic groups, phosphate residues (Phosphoproteins) as well as lipids in varying proportions(Lipoproteins), Nucleic acids (Nucleoproteins; Viruses), sugar residues (Glycoproteins) and polysaccharides(Proteoglycans). Such modifications, which are usually introduced co- or post-translationally(post-translational protein modification) have a major influence on the properties of proteins. They influence e.g. their stability, solubility, hydrophobicity and - in the case of reversible modifications - their activity. The activity of many proteins, e.g. digestive enzymes (digestion) or blood coagulation factors, can also be modified by breaking down inactive precursors. Mostly loosely bound and therefore exchangeable low molecular weight components of proteins are the ions required to neutralize charged groups as well as Enzyme proteins (Enzymes) the coenzymes, inhibitors and activators.
As Primary structure of proteins (see Fig. 1) - identical to the term Amino acid sequence - one denotes the linear, written order of the individual amino acid residues of each protein. It is genetically determined by the base sequence of the respective genes (deoxyribonucleic acids, one-gene-one-enzyme hypothesis, genetic code, ribonucleic acids, translation). The enormous variety of possible primary structures can be illustrated by the following consideration: According to the laws of combinatorics, 20 result for the chains made up of n amino acidsn theoretical possibilities. This means that for the relatively small chain length of 100 amino acids alone, 20100 = 10130 Theoretical possibilities exist, of which only a tiny fraction has been realized in the organisms living today (but also if one includes all the species that have appeared in the course of the earth's history) (in view of the fact that for the entire universe it is about 1080 estimated number of elementary particles is the number 10130 "Super astronomical high"). The similarity of the primary structures of homologous proteins (sequence homology), especially those that are conserved to a greater extent, such as histones or cytochromes, has become a criterion for establishing Sequence pedigrees - analogous to the family trees on the basis of phenotypic characteristics (family tree) - proven and gives insight into molecular evolution. Since the primary structure significantly influences the folding and thus the higher-level structures of proteins (see below), their elucidation offers the possibility of Structure prediction and gives insights into how proteins work. In addition, the amino acid sequence contains signals for the localization of proteins in the cell (Protein transport) and for processing (e.g. glycosylation, proteolytic activation). Changes in the primary structure of proteins can lead to diseases, targeted changes in the primary structure are used to generate proteins with correspondingly changed properties and effects (protein engineering).
As Secondary structures of the proteins, all periodically recurring superstructures caused by hydrogen bonds (hydrogen bonds) are summarized, with hydrogen bonds between residues close to the sequence Screw or Helix structures (Helices), through H-bonds between peptide chains far from the sequence, parallel or antiparallel to the Leaflet structures form. The latter can also arise between different peptide chains. Finally, one of the secondary structures is the helical structure of collagen, which is made up of 3 parallel chains, since here, too, regularly recurring hydrogen bonds bring about stability. The most common screw structure is the α-helix (Alpha-Helix; see Fig. 1 and see Fig. 2), which is independent of the twisting sense, which is, however, right-handed in natural polypeptides, also called α structure referred to as. The different substituents of the individual amino acid residues protrude outwards in the screw structures and can therefore interact with the surrounding medium or with the substituents of more distant amino acids of the same chain or also substituents of other chains. The substituents (side residues) that determine the script-like character are accessible from the outside in the helical protein structures - in contrast to the DNA double helix, in which the bases that determine the script-like character are "buried" inside (ä deoxyribonucleic acids III). The amino acid proline is the only one of the 20 amino acids to have a ring-bound and therefore secondary amino group (amino acids) and therefore cannot adopt the configuration required for helical hydrogen bonds. For this reason, α-structures are interrupted at all proline positions of a peptide chain (function of Proline as so-called Helix breaker), which is important for the kinking of helical structures in the formation of tertiary structures (see below). Formed by inter- or intramolecular antiparallel attachment of peptide chains Leaflet structuresthat one as β structures (Beta sheet) denotes (antiparallelism). The substituents of the individual amino acid residues in the β-structures protrude alternately in the opposite direction with respect to the plane of the sheet (see Fig. 3). The abrupt reversal of the direction of a polypeptide chain, which is necessary for the formation of antiparallel sheet strands, occurs at so-called. β loops which are similar in structure to the hairpin loops of nucleic acids. As a rule, secondary structures do not form over the entire length of peptide chains. For example, myoglobin is made up of over 75% α-structures, which corresponds to a relatively high secondary structure content, while chymotrypsin has an α-helix content of only 8%. As a special case for a protein made up of almost 100% sheet structure, fibroin should be mentioned, whereas most proteins have significantly fewer sheet structure components. The possibility of reversible conversion between the α-helix structure and the sheet structure in keratin is remarkable. The grouping of secondary structural elements into so-called Super secondary structures (e.g. βαβ). Regions that have neither α nor β conformations are called Random ball (also disordered framework conformation or random coil), which are not actually counted among the secondary structures, as they - deviating from the above definition - contain neither hydrogen bonds nor repetitive structures (other definitions: secondary structure).
As Tertiary structure of proteins is the name given to the folding of individual peptide chains into a three-dimensional specific structure, whereby the secondary structures are retained (see Fig. 1). The formation of tertiary structures gives proteins the shape characteristic of their respective functions (structure-function relationship), in particular the specific grooves of the surfaces, such as those required for the binding and conversion of substrate molecules in the active centers of the enzymes. In the folds that take place to form tertiary structures, amino acid residues that are far apart in the primary and secondary structures often come into spatial proximity. Allosteric conversions (allostery) of proteins go hand in hand with refolding of tertiary structures (and as a consequence of this also of the quaternary structures, see below). Tertiary structures are stabilized by intramolecular (intrachenare) Disulfide bonds, but especially due to the alignment of as many hydrophobic and non-polar amino acid residues as possible inside and hydrophilic, particularly ionically structured amino acid residues to the outer surface of the structures. The hydrophobic residues of the inner parts usually fit together seamlessly to form hydrophobic areas in which there are hardly any cavities and which are not accessible even for the relatively small water molecules (water) of the surrounding medium. In contrast, the polar residues of the amino acids on the surface form hydrogen bonds with the water molecules (water) of the medium and thus lead to the so-called. Hydration shell of proteins. At Membrane proteins Even non-polar amino acids occupy a considerable part of the outward-facing positions and thus enable them to be anchored in the hydrophobic inner areas of the membrane bilayers (liquid mosaic model, membrane). Another tertiary structural element is the so-called Domains, compact areas with mostly independent functions, which are often coded by their own exons.
As Quaternary structure This is the term used to describe the structure of many proteins from 2 or more identical or different peptide chains (subunits, protomers) which, after formation and preservation of the secondary and tertiary structures, accumulate to form multimeric proteins (see Fig. 1). The monomeric forms are mostly inactive. They are usually attached to one another through non-covalent bonds (ionic bonds, hydrophobic interactions, hydrogen bonds), whereby the interacting surface structures of the individual subunits fit into one another according to the lock and key principle, and in rare cases also through the formation of intermolecular (= interchenar) disulfide bridges. As a rule, proteins that can be regulated allosterically have a quaternary structure (e.g. hemoglobin) that can be changed by binding an effector. However, there are also a number of proteins that are made up of only 1 peptide chain (e.g. lysozyme, myosin, ribonuclease, bacterial DNA polymerase), which therefore lack a quaternary structure. Among the known proteins with a quaternary structure, those made up of an even number of identical or similar subunits predominate (e.g. chaperonins, glutamine synthetase, hemoglobin). In contrast, proteins with an odd number or differently sized subunits (e.g. immunoglobulins) or with subunits that are active independently of one another (multi-enzyme complexes such as fatty acid synthetase complex, pyruvate dehydrogenase), as well as with regulatory and catalytic subunits (aspartate transcarbamylase, cAMP-dependent protein kinase) are less common. Reasons for the evolution of oligomeric protein complexes (oligomers) are, among other things, that the direct interaction of different functional areas enables cooperativity and feedback mechanisms (end product inhibition) between the subunits as well as the channeling of metabolites (metabolic channeling).
Properties: According to their molecular size and shape (dimensions 2–100 nm), the proteins belong to the Colloids (colloid). They do not dialyze (dialysis), do not form real solutions, show the Tyndall effect and have a relatively high viscosity. Proteins carry a large number of ionizable groups. The ampholyte nature (ampholytes) of proteins is based on the simultaneous presence of free acidic and basic groups. It is of crucial importance for their buffer effect (buffer) in biological systems. The state of charge (electrical charge) of the entire molecule depends on the pH value of the surrounding medium (see Fig. 4). In a strongly acidic medium, proteins are present as poly cations, in a strongly basic medium as poly anions, the excess charge of which causes increasing hydration and solubility. The sense of charge is responsible for the direction of migration in the electric field. At the isoelectric point the proteins have no net charge, solubility and hydration reach a minimum. Such properties are used in the various methods for protein purification (see below). The superstructures dissolve through the action of certain agents (e.g. agents that dissolve hydrogen bonds such as urea and guanidinium hydrochloride together with mercaptoethanol or detergents such as SDS, which dissolve hydrophobic interactions), but also through non-physiological conditions such as high temperatures and changes in pH value (= Sum of secondary, tertiary and quaternary structures) of most proteins, the primary structure being retained in the form of a random coil. This as denatured (Denaturation) denoted proteins show opposite the native Proteins (native) completely changed physical and chemical properties. Denatured proteins are usually insoluble in water and flocculate (precipitation), unless they are artificially kept in solution by detergents such as SDS. The biological activity, e.g. the catalytic activity of enzyme proteins, is usually lost due to denaturation. In the case of simple proteins, denaturation can be reversed by a controlled termination of the denaturing conditions (e.g. by dialysis of urea and mercaptoethanol) without the aid of other factors (Renaturation; see Fig. 5), which proves that the information for the formation of three-dimensional structures is contained solely in the amino acid sequences - i.e. ultimately in the nucleotide sequences of the genes concerned. It is essential for the function of proteins that the difference in free energy (enthalpy) between the unfolded and the folded state is so small (about 40 kJ / mol for a protein with 100 amino acids) that the contribution of the individual amino acid residues to the The stability of the protein is on average below the thermal energy (2.5 kJ / mol at room temperature). This facilitates protein folding and protein transport through membranes and gives the native protein the necessary flexibility for conformational changes.
Protein folding: The spontaneous folding of the proteins to the superstructures - be it during the synthesis or through renaturation in the test tube - cannot take place by chance processes by "trying out" all theoretically possible folding conformations, since this would take too long: If each amino acid residue had only 3 possible conformations, their "Test" only 10–13 s, the time required for a 100 amino acid peptide would be 3100 Â · 10–13 s = 5 Â · 1047 Â · 10–13 s = 5 Â · 1034 s = 1.6 Â · 1027 Years! Since the time required for the folding is in the range of seconds (or at most minutes), the primary structures obviously contain information for the shortest possible folding path to the native end conformation. The native protein conformation apparently also represents the thermodynamically most favorable conformation, which suggests the spontaneous folding of the proteins from the primary structure, as could also be understood for some proteins in vitro. A basic principle is the progressive stabilization of intermediate products of the folding, which come close to the native conformation. This happens through interactions that also stabilize the finished protein. However, since the contribution of the individual amino acid residue to the stability of the protein is very small (see above), intermediate products of the folding process can be lost. Conversely, intermediate products that do not lead to a native form can be energetically more favorable and represent so-called kinetic traps. Such problems can be the reason why some proteins cannot be renatured or folded in vitro and in vivo, or only with difficulty. The folding process begins with the formation of short sections (about 8-15 residues) on α-helices, β-sheets and β-loops. The amino acids involved usually form autonomous folding units, which would also fold as an independent peptide to form the corresponding structure. These folding units serve as cores to stabilize other ordered regions, whereby cores can be formed and dissolved within milliseconds (see Fig. 6). Cores that belong to the native conformation persist and grow cooperatively, e.g. through the formation of super-secondary structures and entire domains. When globular proteins fold, an as "Molten globule" designated intermediate stage with extensive secondary structure, but a disordered tertiary structure, in which hydrophobic core areas assemble into a compact but still flexible structure and which reaches the compact tertiary structure of the monomeric protein with minor conformational changes. In the case of proteins that are stabilized by disulfide bonds, only native disulfide bonds appear in the course of the folding. In principle, different regions can be stabilized at different times in the course of the folding process and folding paths can be taken via various intermediate products. To form oligomeric proteins, only the monomers involved are assembled into the native quaternary structure via a few intermediate stages. In addition to the problems already mentioned, the relatively high protein concentrations and temperatures in the cell, which result in constant interactions between intra- and inter-polypeptide surfaces, are problematic for protein folding in vivo. In protein folding in connection with protein synthesis, protein transport through membranes and renaturation after stressful situations, as well as in the assembly of subunits into higher-order structures, this inevitably leads to incorrect folding and aggregation. Today we know that so-called molecular chaperones (Proteins binding polypeptide chains) assisting in protein folding or in the transition of polypeptide chains from the denatured to the native state as well as in the assembly of protein subunits (assisted self-assembly). Molecular chaperones have no classical catalytic effect and no influence on the native conformation, rather they prevent hydrophobic interactions and incorrect aggregations of intra- and inter-polypeptide surfaces of the substrate proteins. The protein disulfide isomerase for the formation of correct disulfide bridges in the non-reducing environment of the endoplasmic reticulum and the peptidyl-prolyl-cis-trans-isomerase are catalytically active folding helper proteins cis / trans-Isomerization of Proline Peptide Bonds.
Classification: The proteins can be classified according to several criteria such as composition and shape (see table), occurrence and function. - After composition A distinction is made between simple proteins, which are only made up of proteinogenic amino acids, and composite proteins (conjugated proteins) which, in addition to the protein portion, contain a mostly chemically bound non-protein component. - After shape a distinction is made globular and fibrillar proteins. Globular proteins (spheroid proteins) are spherical and soluble in water and dilute salt solutions. This is based on the charged, hydrophilic amino acid residues located on the surface of the molecule, which - surrounded by a hydration shell - ensure close contact with the solvent. The fibrillar proteins (Fiber proteins, structural proteins, Scleroproteins) are practically insoluble in water and salt solutions. The polypeptide chains are arranged parallel to one another and form long fibers. - After this Occurrence In the organism groups, a distinction must be made between human, animal, plant and microbial proteins, with further subdivisions according to their occurrence in certain organs (e.g. blood proteins, serum proteins, milk proteins, muscle proteins, storage proteins from plant seeds) and in certain cell fractions (cytoplasmic proteins, ribosome proteins, core proteins, Membrane proteins, chloroplast proteins and mitochondrial proteins) or viruses (capsid). - After function the proteins are divided into: 1) Enzyme proteins (Enzymes) that catalyze the biochemical reactions of metabolism. 2) Transport proteins for the transport of oxygen, fatty acids, hormones, metal ions and electrons (e.g. hemoglobin, myoglobin, transferrin, ceruloplasmin, serum albumin, cytochromes) or Translocator proteins membrane transport (translocator). 3) Storage proteins for the storage of metal ions (e.g. hemosiderin, ferritin) or Storage proteins, which secure the amino acid reserves of the organism (e.g. egg albumin, casein, gliadin, gluteline, prolamine, zein). 4) Contractile Proteinswhich cause the coordinated mobility of certain organs (e.g. muscles; muscle proteins), organelles (e.g. cilia) or other cellular structures (e.g. chromatids) (e.g. actin, myosin, microtubules, dynein, kinesin; motor proteins). 5) structure resp. Scaffold proteins (Scleroproteins) as an essential component of supporting tissue and connective tissue (e.g. collagen, elastin, keratins). 6) Defense proteins for cellular defense reactions (e.g. immunoglobulins). 7) Receptor proteins for the transmission of signals caused by hormones or neurotransmitters. 8th) Regulator proteinsthat are involved in regulatory processes of gene activation (gene regulation) and cell growth (e.g. activator proteins and repressor proteins [repressors], proteohormones, transcription factors, growth factors). 9) Cell surface proteins that enable one cell type to be recognized by another and therefore play a role in morphogenesis and the recognition of foreign tissue (e.g. adhesins, blood group antigens, CD markers). 10) Blood clotting and fibrinolysis factors. This multitude of highly specific functions is understandable in view of the structural diversity of proteins. This also results in the high proportion of organic components in protein (over 50%) that the cells of all organisms (including viruses) have. -

Important techniques and parameters for characterizing proteins:

a)Quantitative determination and Verification procedure: These are based either on color reactions (colorimetry, protein determination) that are specific for certain amino acid residues, on the measurement of the absorption (absorption spectroscopy, extinction) at 280 nm wavelength, which is caused by the aromatic amino acid residues, or on the measurement of the absorption of visible light Chromoproteins. In the case of color reactions, solutions of calibration proteins (mostly bovine serum albumin) of known concentration are made to react in parallel batches and the concentrations of the proteins to be examined are determined by comparing the color intensities. These methods can be used for most proteins, but do not allow any distinction between individual proteins or protein mixtures. In contrast, immunological methods (immunassays), e.g. immunoprecipitation (agar diffusion test, immunoelectrophoresis) or the Western technique (blotting techniques), are particularly specific and sensitive detection methods for individual proteins in complex mixtures, such as blood serum (serum proteins) and cell breakdowns. The high specificity of these detection methods is based on the action of proteins as antigens or their binding to antibodies (immunoglobulins). Proteins marked (labeling) by incorporating radioactive groups by chemical methods or radioactive amino acids during protein synthesis can be detected e.g. by means of autoradiography and radioimmunoassays. Enzyme proteins can also be specifically detected by the reactions they catalyze, the most common method being the optical test.
b)cleaning and Insulation: Soluble intracellular proteins are preparatively purified from the mostly very complex mixtures, such as those present in homogenates after cell disruption. In the case of extracellular proteins, e.g. from body fluids or supernatants from cell cultures, cells and other insoluble components must first be removed. Insoluble proteins, such as most integral membrane proteins, have to be solubilized by detergents such as CHAPS or SDS or prevented from developing hydrophobic interactions by means of chaotropic compounds before starting a purification process, whereby the preservation of the native state is usually no longer possible. In the case of structural proteins (scleroproteins), which are also insoluble, it usually makes sense to first remove all soluble proteins before enrichment. Recombinant proteins are quite easy to purify because they are available in relatively large quantities and the purification strategy is tailored to the type of their expression (eg fusion proteins with specific tags) and release (eg in the form of inclusion bodies, secretion in culture medium) can (expression system). The actual purification process of the proteins takes place using their size, solubility, charge, specific binding properties and biological activity by combining different methods: By means of fractional centrifugation (density gradient centrifugation and differential centrifugation) and fractional precipitation (precipitation), e.g. with ammonium sulfate, ethanol (Cohn Fractionation) or trichloroacetic acid, a pre-separation is carried out. Further purification steps are based on chromatographic (chromatography) and electrophoretic (electrophoresis) separation methods, including ion exchange chromatography, adsorption chromatography, affinity chromatography, metal chelate affinity chromatography, reversed-phase chromatography, hydrophobic interaction chromatography, gel filtration, preparative gel electrophoresis and isoelectric focusing. Basically, the strategy of the individual cleaning steps is either to remove unwanted components or to enrich the target component. Between the individual cleaning steps, it is often necessary to adjust the ionic strength or buffer composition of the solutions, which can be achieved, for example, by means of dialysis, ultrafiltration or gel filtration. A concentration of solutions is also possible by dialysis and ultrafiltration as well as by precipitation. The removal of detergents during the purification of hydrophobic proteins (whereby their solubility and activity is lost) can be done, among other things, by extraction with chloroform / methanol or by reversed phase chromatography. A protein that has been purified for homogeneity (uniformity) is of essential importance for the subsequent analysis of structure and function.
c)Purity criteria: A "pure" protein can also contain inorganic salts, other small organic molecules (e.g. substrates, coenzymes) and water. The degree of purity of proteins or the composition of protein mixtures is usually determined by gel electrophoresis, whereby either one-dimensional methods such as disk electrophoresis, isoelectric focusing and SDS polyacrylamide gel electrophoresis are used or to dissolve very complex protein mixtures (up to over 1000 different proteins) high-resolution two-dimensional gel electrophoresis is used. Criteria for the purity of proteins are also uniform sedimentation speed (S-value; sedimentation) during ultracentrifugation (ultracentrifuge), integer number of the amino acid composition, sequencing (sequencing), linear progression up to the saturation point in the solubility diagram and crystallizability (protein crystallization). In the case of enzymes, the activity criteria (pH and temperature optimum, substrate specificity, kinetic behavior) are added as further purity criteria.
d)Relative molecular weights (“Molecular Weights”) and Chain lengths: These can be determined at least approximately with simultaneous denaturation by comparing the running speeds of the peptide chains to be examined with the running speeds of marker proteins (markers) of known molecular weight in SDS-polyacrylamide gel electrophoresis. The molecular masses of native proteins can be estimated from the sedimentation rates in ultracentrifugation (especially in density gradient centrifugation) and the elution volume in gel filtration. The chain lengths (= number of amino acid residues per peptide chain) can be approximately calculated from the molecular weights by dividing them by the number 110, the mean molecular weight of the 20 amino acid residues. Conversely, if the amino acid composition and the number of tryptic peptides or the amino acid sequence of a protein are known, the molecular mass can be determined by calculation. Various methods of mass spectrometry meanwhile allow the determination of the relative molecular masses of the smallest amounts of protein with high mass resolution and a high sample throughput, which is of essential importance in the context of proteomics.
e)Number of peptide chains (and their molecular weights): These can be determined directly after denaturation by SDS-polyacrylamide gel electrophoresis, provided that chains of different lengths and / or different compositions are involved in the construction of a purified protein. In the case of oligomeric proteins made up of identical chains, the chain number can be determined by comparing the molecular mass of the native protein (can be determined from the sedimentation rate) with the molecular mass of the denatured protein (can be determined from SDS polyacrylamide gel electrophoresis). In the case of a protein made up of 4 identical subunits, these molecular weights differ e.g. by a factor of 4.
f)Amino acid composition: This is determined in the amino acid analyzer after hydrolysis of the protein to the amino acids.
G)Amino acid sequence: To determine the amino acid sequence of a protein directly, it is first split into defined partial peptides - after the disulfide bonds have been split - by the limited action of proteases or by the cyanogen bromide reaction and these are separated chromatographically. The amino acid sequences of all partial peptides are then determined individually by the cyclic reaction sequences of Edman's degradation beginning at the amino terminus (e.g. in the gas phase sequenator) and / or by mass spectrometry. (C-terminal end groups are determined separately by chemical or enzymatic degradation methods or by mass spectrometry.) Finally, the amino acid sequence of the entire chain can be deduced from a series of overlapping partial peptides. As a rule, today amino acid sequences of proteins are derived from the nucleotide sequences of the genes concerned according to the rules of the genetic code, because with the rapid development and expansion of methods in the context of genetic engineering and the genome project, the sequence analysis of DNA is technically easier than that of proteins ( DNA sequencer; sequencing). The direct amino acid sequencing is limited to easily accessible or selected partial peptides for random checks of the amino acid sequences derived from nucleotide sequences or for the determination of amino acid sequences that cannot be derived, such as the exon boundaries (exon, mosaic genes).
H)Structural analysis: The Secondary structures of proteins can be detected e.g. by means of CD spectroscopy and infrared spectroscopy. Tertiary structures The secondary and quaternary structures are usually determined by X-ray structure analysis of isomorphically crystallized heavy metal atom derivatives of the protein in question, while by measuring the intrinsic angular momentum (spin) of atomic nuclei with the help of nuclear magnetic resonance spectroscopy, in addition to determining the protein structure (in solution), the detection is dynamic Phenomena on proteins is possible. Quaternary structures of proteins can be analyzed by electron microscopic methods (electron microscope) including various methods for image analysis, image processing and 3D reconstruction (imaging methods). Methods with a focus Structure-function analysis are - in addition to almost all spectroscopic methods - the chemical modification of functional groups, the introduction of reporter groups (e.g.Fluorochromes; Fluorescence labeling, fluorescence spectroscopy), protein cross-link, peptide synthesis and the targeted modification of the amino acid sequence through in vitro mutagenesis of the coding gene (protein engineering). It is also often necessary to obtain sufficient quantities of a protein for analysis using genetic engineering methods. -

On the historical development of protein research:Biochemistry (history of); for the synthesis of proteins:Translation, endoplasmic reticulum, export protein synthesis; to break down proteins:Proteases, protein degradation, proteolysis.
Significant research in the field of proteins was carried out by C.B. Anfinsen, C.G.R. Berg, C.L. by Berthollet, T.R. Cech, J. Deisenhofer, Em.H. Fischer, H. Fraenkel-Conrat, A.D. Hershey, E.F.I. Hoppe-Seyler, R. Huber, J.C. Kendrew, A. Klug, A. Kossel, O. Loewi, F. Magendie, R.B. Merrifield, H. Michel, G.E. Palade, L.C. Pauling, M.F. Perutz, W. Prout, F. Sanger, J.B. Sumner. - Bioinformatics, biophysics, calorific value, nutritional physiology (tab.), Essential food components, genomics, nuclear transport of proteins, molecular biology, food, nutrients, nutritional value, prions, protein determination, protein-DNA interaction, protein-energy deficiency syndrome, protein family, protein crystallization, Protein-ligand complex, protein-protein interactions, protein secretion, protein sequenator