Infrared spectra and structure of synthetic polytripeptides

A number of polytripeptides related to collagen, namely, (Gly-Pro-Pro)_n, (Gly-Pro-Hyp)_n, (Gly-Hyp-Hyp)_n, (Gly-Pro-Ala)_n, (Gly-Pro-Leu)_n, (Gly-Pro-Gly)_n,(Gly-Ala-Pro)_n, (Gly-Ala-Hyp)_n, (Ala-Pro-Pro)_n, and (Ala-Hyp-Hyp)_n were investigated by the method of ir spectroscopy and hydrogen-deuterium kinetics. Strength and order of interpeptide hydrogen bonds of the polytripeptides in a triple-helical conformation were found to depend on the amino acid composition and residue sequence in the triplets. Correlation of X-ray diffraction and spectroscopic data for (Gly-Pro-Hyp)_n showed that the increase of the helix parameter in the process of dehydration is accompanied with the weakening of interpeptide hydrogen bonds. Influences of bound water on the length and order of interchain hydrogen bonding was also examined. It was shown that the incorporation of water molecules into the triple helix depends on the amino acid composition and residue sequence. Synthetic models and native collagens were compared.     

Formation of a hydrate structure in the collagen-like triple helix upon hydration

By the IR-spectroscopy method successive stages of hydrate envelope formation of the collagen-like triple-helical structure of the monodisperse synthetic polytripeptide Z-(Gly-Pro-Pro)8-OMe were studied. The multistep-type process is followed by isomorphic transitions of the triple-helical structure and by the increasing of hydrogen bond strength.     

An energetic evaluation of a "Smith" collagen microfibril model.

An energy minimized three-dimensional structure of a collagen microfibril template was constructed based on the five-stranded model of Smith (1968), using molecular modeling methods and Kollman force fields (Weiner and Kollman, 1981). For this model, individual molecules were constructed with three identical polypeptide chains ((Gly-Pro-Pro) _n , (Gly-Prop-Hyp) _n , or (Gly-Ala-Ala) _n , wheren=4, 12, and 16) coiled into a right-handed triple-helical structure. The axial distance between adjacent amino acid residues is about 0.29 nm per polypeptide chain, and the pitch of each chain is approximately 3.3 residues. The microfibril model consists of five parallel triple helices packed so that a left-handed superhelical twist exists. The structural characteristics of the computed microfibril are consistent with those obtained for collagen by X-ray diffraction and electron microscopy. The energy minimized Smith microfibril model for (Gly-Pro-Pro)₁₂ has an axial length of about 10.2 nm (for a 36 amino acid residue chain), which gives an estimated D-spacing (234 amino acids per chain) of approximately 66.2 nm. Studies of the microfibril models (Gly-Pro-Pro)₁₂, (Gly-Pro-Hyp)₁₂, and (Gly-Ala-Ala)₁₂ show that nonbonded van der Waals interactions are important for microfibril formation, while electrostatic interactions contribute to the stability of the microfibril structure and determine the specificity by which collagen molecules pack within the microfibril.     

Proton transfer and polarizability of hydrogen bonds in proteins coupled with conformational changes. I. Infrared investigation of poly(glutamic acid) with various N Bases

The nature of hydrogen bonds formed between carboxylic acid residues and histidine residues in proteins is studied by ir spectroscopy. Poly(glutamic acid) [(Glu)_n] is investigated with various monomer N bases. The position of the proton transfer equilibrium OH…?N ? O^?…?H⁺N is determined considering the bands of the carboxylic group. It is shown that largely symmetrical double minimum energy surfaces are present in the OH…?N ? O^?…?H⁺N bonds when the pK_a of the protonated N base is two values larger than that of the carboxylic groups of (Glu)_n. Hence OH…?N ? O^?…?H⁺N bonds between glutamic and aspartic acid residues and histidine residues in proteins may be easily polarizable proton transfer hydrogen bonds. The polarizability of these bonds is one to two orders of magnitude larger than usual electron polarizabilities; therefore, these bonds strongly interact with their environment. It is demonstrated that water molecules shift these proton transfer equilibria in favor of the polar proton boundary structure. The access of water molecules to such bonds in proteins and therefore the position of this proton transfer equilibrium is dependent on conformation. The amide bands show that (Glu)_n is α-helical with all systems. The only exception is the (Glu)_n-n-propylamine system. When this system is hydrated (Glu)_n is α-helical, too. When it is dried, however, (Glu)_n forms antiparallel β-structure. This conformational transition, dependent on degree of hydration, is reversible. An excess of n-propylamine has the same effect on conformation as hydration.     

High-resolution solid-state 13C-NMR of peptides: a study of chain-length dependence for 3(10)-helix formation

High-resolution solid-state ¹³C-nmr spectra of two series of fully protected oligopeptides, Z-(Aib)_n-OMe (n = 3?8) and Z-(Aib)_n-L-Leu-(Aib)₂-OMe (n = 0?5), were recorded to gain insight into main-chain length dependence for 3₁₀-helix formation. We found that all the oligopeptides examined adopt an incipient or a fully developed 3₁₀-helical structure, as judged from the characteristic splitting of the C_β signals as well as the conformation-dependent displacements of the C_α and C?O peaks.     

Chain length dependent transition of 310- to α-helix of Boc-(Ala-Aib)n-OMe

An apolar synthetic octapeptide, Boc-(Ala-Aib)₄-OMe, was crystallized in the triclinic space group P1 with cell dimensions a = 11.558 Å, b = 11.643 Å, c = 9.650 Å, α = 120.220°, β = 107.000°, γ = 90.430°, V = 1055.889 ų, Z = 1, C₃₄H₆₀O₁₁N₈·H₂O. The calculated crystal density was 1.217 g/cm³ and the absorption coefficient ? was 6.1. All the intrahelical hydrogen bonds are of the 3₁₀ type, but the torsion angles, ? and ψ, of Ala(5) and Ala(7) deviate from the standard values. The distortion of the 3₁₀-helix at the C-terminal half is due to accommodation of the bulky Boc group of an adjacent peptide in the nacking. A water molecule is held between the N-terminal of one peptide and the C-terminal of the other. The oxygen atom of water forms hydrogen bonds with N (1) -H and N (2) -H, which are not involved in the intrahelical hydrogen bonds. The hydrogen atoms of water also formed hydrogen bonds with carbonyl oxygens of the adjacent peptide molecule. On the other hand, ¹H-nmr analysis revealed that the octapeptide took an α-helical structure in a CD₃CN solution. The longer peptides, Boc-(Ala-Aib)₆-OMe and Boc-(Ala-Aib)₈-OMe, were also shown to take an α-helical structure in a CD₃CN solution. An α-helical conformation of the hexadecapeptide in the solid state was suggested by x-ray analysis of the crystalline structure. Thus, the critical length for transition from the 3₁₀- to α-helix of Boc-(Ala-Aib)_n-OMe is 8. © 1993 John Wiley & Sons, Inc.     

Role of proline …︁ proline interactions in the packing of collagenlike poly(tripeptide) triple helices

Conformational energy computations were carried out on the packing of two identical collagenlike poly(tripeptide) triple helices in order to determine the energetics of favorable packing arrangements as a function of composition and chain length. The triple helices considered were [CH₃CO-(Gly-Pro-Pro)_nt-NHCH₃]₃ and [CH₃CO-(Gly-Pro-Ala)_nt-NHCH₃]₃, with n_t = 3, 4, and 5. The packing arrangements were characterized in terms of their intermolecular energies and orientation angles Ω₀ of the axes of the two triple helices. For short triple helices (n_t = 3 or 4), many low-energy orientations, with a wide range of values of Ω₀, can occur. When the triple helices are longer (n_t = 5), the only low-energy packing arrangements of two poly(Gly-Pro-Pro) triple helices are those with a nearly parallel orientation of the two helix axes, with Ω₀ ≈ ?10°. This result accounts for the observed parallel (rather than antiparallel) arrangement of collagen molecules in microfibril assembly and stands in contrast to the preferred antiparallel arrangement of a pair of α-helices. Since the preference for a parallel arrangement of these collagenlike triple helices is less pronounced in the case of poly(Gly-Pro-Ala), it appears that this preference is a consequence of the frequent presence of imino acids in position Y of the Gly-X-Y repeating triplet. In poly(Gly-Pro-Ala), most of the low-energy packing arrangements are parallel, but a few arrangements with low energies and high values of |Ω₀| occur. These packing arrangements have a high energy, however, when Pro is substituted for Ala, and thus they are not accessible for collagen with natural amino (imino) acid sequences. The computations reported here account for some of the characteristic features of collagen packing in terms of the local interaction energies of a pair of triple helices.     

An energetic evaluation of a “Smith” collagen microfibril model

An energy minimized three-dimensional structure of a collagen microfibril template was constructed based on the five-stranded model of Smith (1968), using molecular modeling methods and Kollman force fields (Weiner and Kollman, 1981). For this model, individual molecules were constructed with three identical polypeptide chains ((Gly-Pro-Pro) _n , (Gly-Prop-Hyp) _n , or (Gly-Ala-Ala) _n , wheren=4, 12, and 16) coiled into a right-handed triple-helical structure. The axial distance between adjacent amino acid residues is about 0.29 nm per polypeptide chain, and the pitch of each chain is approximately 3.3 residues. The microfibril model consists of five parallel triple helices packed so that a left-handed superhelical twist exists. The structural characteristics of the computed microfibril are consistent with those obtained for collagen by X-ray diffraction and electron microscopy. The energy minimized Smith microfibril model for (Gly-Pro-Pro)₁₂ has an axial length of about 10.2 nm (for a 36 amino acid residue chain), which gives an estimated D-spacing (234 amino acids per chain) of approximately 66.2 nm. Studies of the microfibril models (Gly-Pro-Pro)₁₂, (Gly-Pro-Hyp)₁₂, and (Gly-Ala-Ala)₁₂ show that nonbonded van der Waals interactions are important for microfibril formation, while electrostatic interactions contribute to the stability of the microfibril structure and determine the specificity by which collagen molecules pack within the microfibril.     

Amide I band of IR spectrum and structure of collagen and related polypeptides

The infrared amide I band of collagens (rat and cod skin) and related compounds (polyproline, polyglycine, and polytripeptides) was studied. Assignment of amide I-band components for polyproline II and polytripeptides (Gly-Pro-Pro)_n and (Gly-Pro-Gly)_n in the solid state and water solution was made. Three amide I components observed in the polypeptide spectra were attributed to three different peptide CO groups in each triplet. On the basis of this assignment, the interpretation of the amide I multicomponent structure in collagen and isomorphous oligo- and polypeptides was attempted. The ordering of intra- and intermolecular hydrogen bonds involving peptide CO groups in collagen and related compounds was discussed.     

Conformational change of the triple-helical structure. III. Stabilizing forces in the triple helix

The analysis of thermal melting curves of (PPG)_n (n = 10, 12, 14, and 15) and (PPG)_n(APG)_m (PPG)_n (2n + m = 15; m = 1, 3, and 5) revealed that the enthalpy and entropy changes accompanying the transition from the random coil to the triple helix are ?2500 cal and ?6.3 e.u. per one mole of the tripeptide of the form of Pro-Pro-Gly, and ?3100 cal and ?11.2 e.u. per one mole of the tripeptide of the form of Ala-Pro-Gly. The thermal instability of the triple helix composed of Ala-Pro-Gly sequences, compared to the helix of Pro-Pro-Gly sequences, is due to the larger entropy change of Ala-Pro-Gly (?11.2 e.u.) compared to that of Pro-Pro-Gly (?6.3 e.u.), not from the difference in the enthalpy change. The difference in the enthalpy change between Pro-Pro-Gly and Ala-Pro-Gly arises from the hydrophobic bond between two pyrrolidine rings of proline residues formed in the triple helix. Since the enthalpy change for the formation of hydrophobic bonds is positive, it is also concluded that only one hydrogen bond is formed in a tripeptide unit, regardless of the amino acid sequence. The enthalpy change for the formation of this hydrogen bond is ?3100 cal/mol, and that of the hydrophobic bond between two pyrrolidine rings is +600 cal/mol.     

Crystal Structure of 2′-Deoxycytidine Hemidihydrogenphosphate Reveals C+·C Base Pairs and Tight,Hydrogen-Bonded (H2PO4 −)∞ Columns (1)

Abstract

2′-Deoxycytidine hemidihydrogenphosphate has been crystallized in the hexagonal space group P6₂ with α=25.839(3), c = 12.529(1) Å. The structure has been solved using the Patterson search method. The asymmetric unit contains two protonated, base-paired 2′-deoxycytidine dimers and two H₂PO₄ ^? anions. The C⁺·C base pairs are composed of a protonated and a neutral species each and are triple H-bonded, the central N(3)…N(3) bonds being 2.850(7) and 2.884(5) Å. The conformations of the four nucleosides fall in the same category (sugar puckers 2·-endo, glycosidic links anti) but in one of them the glycosidic torsion angle is quite low with consequences in other geometrical parameters. The H₂PO₄ ^? anions are located on twofold axes and form two types of tight columns with P…P separations about 4.18 Å The neighboring units along a column are linked via two very short O…H…O hydrogen bonds (O…O about 2.49 Å) leading to effective equalization of the P-O bonds. The base pairs of the two dC⁺·dC cations are coplanar and form layers perpendicular to the phosphate columns repeating every c/3. Within the layers, the dimers form a network through 0(5′)…O(2) hydrogen bonds but their primary intermolecular interactions have the form of H-bond anchors [N(4)-H…O-P and 0(3′)-H…O-P] to the phosphate groups.     

The role of hydroxyproline in collagen folding: conformational energy calculations on oligopeptides containing proline and hydroxyproline

We have observed that the rate of folding of the enzymatically hydroxylated form of poly(Gly-Pro-Pro) into the triple-helical conformation is considerably higher than that of the unhydroxylated polypeptide [R. K. Chopra and V. S. Ananthanarayanan (1982) Proc. Natl. Acad. Sci. USA 79 , 7180–7184]. In this study, we examine a plausible kinetic pathway for triple-helix formation by selecting peptide models for the unhydroxylated collagen molecule, and computing their conformational energies before and after proline hydroxylation. Starting with the available data on the preferred conformations of proline- and hydroxyproline-containing peptide sequences, energy minimization was carried out on the following pairs of peptides: Gly-Ala-Pro-Gly-Ala and Gly-Ala-Hyp-Gly-Ala; Gly-Pro-Pro-Gly-Ala and Gly-Pro-Hyp-Gly-Ala; Gly-Ala-Pro-Gly-Ala-Pro and Gly-Ala-Hyp-Gly-Ala-Hyp. It was found that, with each pair of peptides, the energetically most favorable conformation (I) has an extended structure at the Gly-Ala or Gly-Pro segment and a β-bend at the Pro-Gly or Hyp-Gly segment. In the Hyp-containing peptides, this conformation is further stabilized by a (Hyp_{i + 2})OH…OC(Gly_i) hydrogen bond. Conformation I is lower in energy by about 6–13 kcal/mol of the peptide than the fully extended conformations that resemble the single collagen polypeptide chain and contain no intramolecular hydrogen bond. In contrast to the proline counterpart, the hydroxyproline-containing peptides are found capable of adopting a partially extended conformation that does not contain the β-bend but retains the (Hyp)OH…OC(Gly) hydrogen bond. The energy of this conformation is intermediate between conformation I and the fully extended conformation. The continuation of the β-bend along the chain is restricted by stereochemical constraints that are more severe in the latter two pairs of peptides than in the first pair. Such a restriction may be considered to trigger the “unbending” of the minimum energy conformation leading to its straightening into the fully extended conformation; the latter, in turn, would lead to triple-helix formation through favorable interchain interactions. We propose that the partially extended conformation in the Hyp-containing peptides could serve as a kinetic intermediate on the way to forming the fully extended conformation. Because of the (Hyp_{i + 2})OH…OC(Gly_i) hydrogen bond, this conformation would also serve to lock the trans geometry at the Gly-Ala(Pro) and Ala(Pro)-Hyp peptide bonds, thereby enhancing the rate of their helix formation. A scheme for collagen folding in proposed on the basis of these results.     

Proton polarizability and proton transfer in histidine-phosphate hydrogen bonds as a function of cations present: ir investigations

(L -His)_n- dihydrogen phosphate systems are studied by ir spectroscopy in the presence of various cations and as a function of the degree of hydration. Ir continua indicate that (I) OH … N ? O^?…H⁺N (IIR) hydrogen bonds are formed and that these bonds show high proton polarizability, which increases from the Li⁺ to the K⁺ system. In the K⁺?system, His-P_i-P_i chains are formed, showing particularly high proton polarizability due to collective proton motion within both hydrogen bonds. The OH N ? O^?…H^?N equilibria are determined from ir bands. With the Li⁺ system, 55% of the protons are present at the histidine residues; this percentage is smaller with the Na⁺ system (41%), and amounts to only 32% with the K⁺ system. With the increasing degree of hydration the removal of the degeneracy of ν_as?PO^2?₃ vanishes, indicating loosening of the cations from the phosphates. Nevertheless, the hydrogen bond acceptor O atom becomes more negative; a shift of the equilibrium to the right is observed in the OH… N ? O^?…H⁺N bond. This is explained by the strong interaction of the dipole of the hydrogen bonds with the water molecules. All these results show that protons can be shifted easily in these hydrogen bonds due to their high proton polarizability. The transfer equilibria can be controlled easily by local electrical fields. In addition, these results may be of significance when phosphates interact with proteins.     

Proton transfer and polarizability of hydrogen bonds formed between cysteine and lysine residues

(L -Cys)_n + N-base systems and (L -Cys)_n + (L -Lys)_n systems were studied by ir spectroscopy. It is shown that in the water-free systems, SH ?N ? S^? ?H⁺N hydrogen bonds are formed. With the (L -Cys)_n + N-base systems, both proton-limiting structures in the SH ?N ? S^? ?H⁺N bonds have equal weight when the pK_a of the protonated N-base is 2 pK_a units larger than that of (L -Cys)_n. The same is true with the water-free (L -Cys)_n + (L -Lys)_n system. Thus, with regard to the type of proton potentials present, these hydrogen bonds are proton-transfer hydrogen bonds showing very large proton polarizabilities. This is confirmed by the occurrence of continua in the ir spectra. Small amounts of water open these hydrogen bonds and increase the transfer of the proton to (L -Lys)_n. In the (L -Lys)_n + N-base systems, with increasing proton transfer the backbone of (L -Cys)_n changes from antiparallel β-structure to coil. In (L -Cys)_n + (L -Lys)_n, the conformation is determined by the (L -Lys)_n conformation and changes depending on the chain length of (L -Lys)_n. Finally, the reactivity increase in the active center of fatty acid synthetase, which should be caused by the shift of a proton, is discussed on the basis of the great proton polarizability of the cysteine–lysine hydrogen bonds.     

Asparagine and glutamine differ in their propensities to form specific side chain-backbone hydrogen bonded motifs in proteins

Short range side chain‐backbone hydrogen bonded motifs involving Asn and Gln residues have been identified from a data set of 1370 protein crystal structures (resolution ≤ 1.5 Å). Hydrogen bonds involving residues i ? 5 to i + 5 have been considered. Out of 12,901 Asn residues, 3403 residues (26.4%) participate in such interactions, while out of 10,934 Gln residues, 1780 Gln residues (16.3%) are involved in these motifs. Hydrogen bonded ring sizes (C_n, where n is the number of atoms involved), directionality and internal torsion angles are used to classify motifs. The occurrence of the various motifs in the contexts of protein structure is illustrated. Distinct differences are established between the nature of motifs formed by Asn and Gln residues. For Asn, the most highly populated motifs are the C₁₀ (CO^δ_i …NH_{i + 2}), C₁₃ (CO^δ_i …NH_{i + 3}) and C₁₇ (N^δH_i …CO_{i ? 4}) structures. In contrast, Gln predominantly forms C₁₆ (CO^ε_i …NH_{i ? 3}), C₁₂ (N^εH_i …CO_{i ? 2}), C₁₅ (N^εH_i …CO_{i ? 3}) and C₁₈ (N^εH_i …CO_{i ? 4}) motifs, with only the C₁₈motif being analogous to the Asn C₁₇structure. Specific conformational types are established for the Asn containing motifs, which mimic backbone β‐turns and α‐turns. Histidine residues are shown to serve as a mimic for Asn residues in side chain‐backbone hydrogen bonded ring motifs. Illustrative examples from protein structures are considered. Proteins 2012; © 2011 Wiley Periodicals, Inc.     

Structurally symmetrical,easily polarizable hydrogen bonds between side chains in proteins and proton-conducting mechanisms. III

(L -Cys)_n, (L -Lys)_n, and (L -Glu)_n were studied by ir spectroscopy in terms of their degree of deprotonation or protonation. It is shown that structurally symmetrical, easily polarizable SH ?S^? ? ^?S ?HS, N⁺H ?N ? N ?H⁺N, and OH ?O^? ? ^?O ?HO hydrogen bonds are formed between the side chains. The different wave number distributions of the ir continua caused by these hydrogen bonds show that the barrier in the double-minimum proton potential decreases in the series of these hydrogen bonds. The stability of these hydrogen bonds against hydration increases in this series. The OH ?O^? ? ^?O ?HO bonds are not broken by small amounts of water. With (L -Cys)_n the formation of easily polarizable hydrogen bonds and a β-structure–coil transition are strongly interdependent. As a result of this coupling effect, the β-structure–coil transition becomes cooperative. With (L -Glu)_n, the formation of the polarizable hydrogen bonds and the observed conformational change are independent processes. The (L -Glu)_n conformation changes from α-helix to coil only if more than 80% of the residues are deprotonated. Finally, on the basis of the various types of easily polarizable hydrogen bonds, charge shifts in active centers of enzymes and the proton-conducting mechanism through hydrophobic regions of biological membranes are discussed.     

Proton translocation in hydrogen bonds with large proton polarizability formed between a Schiff base and phenols

OH…N ? O^?…H⁺N hydrogen bonds formed between N-all-transretinylidene butylamine (Schiff base) and phenols (1:1) are studied by IR spectroscopy. It is shown that both proton limiting structures of these hydrogen bonds have the same weight with Δ pK_a (50%) = (pK_a protonated Schiff base minus pK_a phenol) = 5.5. With the largely symmetrical systems, continua demonstrate that these hydrogen bonds show great proton polarizability. In the Schiff base + tyrosine system in a non-polar solvent the residence time of the proton at the tyrosine residue is much larger than that at the Schiff base. In CH₂CCl₂ these hydrogen bonds show, however, still proton polarizability, i.e., the position of the proton transfer equilibrium OH…N ? O^?…H⁺N is shifted to and fro as function of the nature of the environment of this hydrogen bond. Consequences regarding bacteriorhodopsin are discussed.     

X-Pro peptides: Synthesis and solution conformation of benzyloxycarbonyl-(Aib-Pro)4methyl ester. Evidence for a novel helical structure

The synthesis of the octapeptide, benzyloxycarbonyl-(α-aminoisobutyryl-L-prolyl)₄-methyl ester [Z-(Aib-Pro)₄-OMe] and an analysis of its solution conformation is reported. The octapeptide is shown to possess three strong intramolecular hydrogen bonds on the basis of studies of the solvent and temperature dependence of NH chemical shifts and rates of hydrogen–deuterium exchange. ¹³C studies are consistent with a structure involving only trans Aib-Pro bonds, while ir experiments support a hydrogen-bonded conformation. The Aib 3, 5, and 7 NH groups are shown to participate in hydrogen bonding. A 3₁₀ helical conformation compatible with the spectroscopic data is suggested. The proposed conformation consists of three type III β-turns with Aib and Pro at the corners and stabilized by 4 → 1 intramolecular hydrogen bonds.     

Molecular dynamics simulations of conformation and chain length dependent terahertz spectra of alanine polypeptides

Terahertz absorption spectra of alanine polypeptides in water were simulated with classical molecular dynamics at 310 K. Vibrational modes and oscillator strengths were calculated based on a quasi-harmonic approximation. Absorption spectra of Ala_n (n = 5, 15, 30) with different chain lengths and Ala₁₅ in coiled and helical conformations were studied in 10–40 cm^? 1 bandwidth. Simulation results indicated both the chain length and the conformation have significant influences on THz spectra of alanine polypeptides. With the increase of chain length, the average THz absorption intensity increases. Compared with the helical Ala₁₅ polypeptide, the THz spectra of coiled one shows stronger absorption peaks. These results were explained from different numbers of hydrogen bonds formed between polypeptides and the surrounding water molecules.     

Bound water in the collagen-like triple-helical structure.

The ir amide bands of the triple-helical polytripeptides and collagens upon hydration of films are investigated. On the basis of our assignment of the amide I components, the formation of hydrogen bonds between the peptide backbone and structural water is studied. The C1O1--HOH hydrogen bonds are found more ordered than the C3O3--HOH hydrogen bonds. The specific incorporation of water in the triple helix is followed by multistep conformational changes and by increasing of the interpeptide hydrogen-bond strength. The formation of the polypeptide hydrate structure depending on the amino acid composition and the chain length is examined.