Modified chemotactic peptides: Synthesis,conformation, and biological activity of for-Thp-Leu-ΔzPhe-OMe

For-Thp-Leu-Δ^zPhe-OMe ( 2 ), an analogue of the chemotactic tripeptide For-Met-Leu-Phe-OMe, containing 4-aminotetrahydrothiopyran-4-carboxylic acid (Thp) and (Z)-2,3-didehydrophenylalanine (Δ^zPhe) as achiral, conformationally restricted mimics of Met and Phe, respectively, has been synthesized. In the crystal the new formyltripeptide adopts a type I β-turn conformation stabilized by a weak H bond between the formylic oxygen and the Δ^zPhe NH. ¹H-nmr analysis based on NH solvent accessibility and nuclear Overhauser effect experiments suggests that the β-turn is not preferred in CDCl₃ solution where a γ-turn, centered at the Thp residue, prevails. The biological activity of 2 has been determined on human neutrophils and compared to that of previously studied analogues. The tripeptide 2 is practically unable to elicit superoxide anion production and lysozyme release, while slight, but not statistically significant activity was induced in chemotaxis. The role of the orientation of the aromatic ring with respect to the backbone adjacent atoms is discussed. © 1994 John Wiley & Sons, Inc.     

Solid-state conformations of α-Aminoisobutyryl-L-prolyl sequences: Crystal structure of Boc-Aib-L-Pro-OBzl

The protected dipeptide Boc-Aib-Pro-OBzl, C₂₁H₃₀N₂O₅, crystallizes in the orthorhombic space group P2₁2₁2₁, with a = 12.820, b = 10.529, c = 16.548Å, and Z = 4. The crystal structure has been solved by direct methods and refined to an R value of 0.074 for 1352 reflections. The Boc-Aib-Pro-OBzl molecule has been shown to adopt an unfolded conformation in the solid state with ?_Aib = 50.5°, Ψ_Aib = 45.3°, ?_Pro = ?64.6°, and Ψ_Pro = 148.1°. The result is in marked contrast with the reported crystal structure of Cbz-Aib-Pro-NHMe, which adopts an intramolecularly hydrogen-bonded β-turn conformation. Comparison with 13 reported conformations of Aib-Pro sequences in the crystalline state revealed that the Aib-Pro sequence adopts an unfolded conformation if the residue that immediately follows the dipeptide sequence possesses no hydrogen available for hydrogen bonding, while a β-turn conformation is preferred if the Pro residue is followed by an NH group. Correlation between pyrrolidine ring puckering of the Pro residue and main-chain conformation in Aib-Pro sequences is discussed.     

Conformational difference between diastereomers of Dnp-Val-Aib-Gly-Leu-pNA studied by x-ray crystal analyses

In order to investigate the Conformational change of the α-aminoisobutyric acid (Aib) containing peptide by the D /L replacement of an amino acid residue, single crystals of two diastereomers, Dnp-L -Val-Aib-Gly-L -Leu-pNA (L -L isomer) and Dnp-D -Val-Aib-Gly-L -Leu-pNA (D -L isomer), were prepared from aqueous methanol solutions as CH₃OH and CH₃OH · H₂O solvates, respectively, and were analyzed by the x-ray diffraction method. Molecular conformation of L -L isomer adopts consecutive two different types of β-turns, a type II′ β-turn bent at Aib-Gly, and a type III β-turn bent at Gly-Leu, stabilized by two intramolecular (Leu) NH …? O?C (Val) and (pNA) NH …? O?C(Aib) hydrogen bonds. In contrast, these two intramolecular hydrogen bonds lead the D -L isomer to a distorted 3₁₀-helix conformation consisting of consecutive two type-III β-turn of Aib-Gly-Leu sequence. The most significant structural difference between these diastereomers is the mutual orientation between the Dnp and pNA chromophores. While the extensive stacking of both the chromophores is intramolecularly formed for the folded conformation of L -L isomer, they are oriented toward an opposite direction in the open conformation of D -L isomer and are intermolecularly stacked with each other. The large separation between these diastereomers observed in the chromatography is discussed in the relation with their Conformational differences. © 1993 John Wiley & Sons, Inc.     

Omega amino acids in peptide design: incorporation into helices

Incorporation of easily available achiral ω-amino acid residues into an oligopeptide results in substitution of amide bonds by polymethylene units of an aliphatic chain, thereby providing a convenient strategy for constructing a peptidomimetic. The central Gly-Gly segment of the helical octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aib-Val-Ome(1) has been replaced by δ-amino-valeric acid (δ-Ava) residue in the newly designed peptide Boc-Leu-Aib-Val-δ-Ava-Leu-Aib-Val-OMe(2). ¹H-nmr results clearly suggest that in the apolar solvent CDCl₃, the δ-Ava residue is accommodated into a folded helical conformation, stabilized by successive hydrogen bonds involving the NH groups of Val(3), δ-Ava(4), and Leu(5). The δ-Ava residue must adopt a gauche-gauche-trans-gauche-gauche conformation along the central polymethylene unit of the aliphatic segment, a feature seen in an energy-minimized model conformation based on nmr parameters. The absence of hydrogen bonding functionalities, however, limits the elongation of the helix. In fact, in CDCl₃, the folded conformation consists of an N-terminal helix spanning residues 1–4, followed by a Type II β-turn at residues 5 and 6, whereas in strongly solvating media like (CD₃)₂SO, the unfolding of the N-terminal helix results in β-turn conformations at Leu(1)-Aib(2). The Type II β-turn at the Leu(5)-Aib(6) segment remains intact even in (CD₃)₂SO. CD comparisons of peptides 1 and 2 reveal a “nonhelical” spectrum for 2 in 2,2,2-trifluoroethanol. © 1996 John Wiley & Sons, Inc.     

Type II β-turn conformation of pivaloyl-L-prolyl-α-aminoisobutyryl-N-methylamide: Theoretical,spectroscopic, and X-ray studies

Pivaloyl-L -Pro-Aib-N-methylamide has been shown to possess one intramolecular hydrogen bond in (CD₃)₂SO solution, by ¹H-nmr methods, suggesting the existence of β-turns, with Pro-Aib as the corner residues. Theoretical conformational analysis suggests that Type II β-turn conformations are about 2 kcal mol^?1 more stable than Type III structures. A crystallographic study has established the Type II β-turn in the solid state. The molecule crystallizes in the space group P2₁ with a = 5.865 Å, b = 11.421 Å, c = 12.966 Å, β = 97.55°, and Z = 2. The structure has been refined to a final R value of 0.061. The Type II β-turn conformation is stabilized by an intramolecular 4 → 1 hydrogen bond between the methylamide NH and the pivaloyl CO group. The conformational angles are ?_Pro = ?57.8°, ψ_Pro = 139.3°, ?_Aib = 61.4°, and ψ_Aib = 25.1°. The Type II β-turn conformation for Pro-Aib in this peptide is compared with the Type III structures observed for the same segment in larger peptides.     

Crystal and molecular structure of benzyloxycarbonyl-α-aminoisobutyryl-L-prolyl methylamide: The observation of an X2-Pro3 Type III β-Turn

The crystal and molecular structure of N-benzyloxycarbonyl-α-aminoisobutyryl-L -prolyl methylamide, the amino terminal dipeptide fragment of alamethicin, has been determined using direct methods. The compound crystallizes in the orthorhombic system with the space group P2₁2₁2₁. Cell dimensions are a = 7.705 Å, b = 11.365 Å, and c = 21.904 Å. The structure has been refined using conventional procedures to a final R factor of 0.054. The molecular structure possesses a 4 → 1 intramolecular N-H—O hydrogen bond formed between the CO group of the urethane moiety and the NH group of the methylamide function. The peptide backbone adopts the type III β-turn conformation, with ?₂ = ?51.0°, ψ₂ = ?39.7°, ?₃ = ?65.0°, ψ₃ = ?25.4°. An unusual feature is the occurrence of the proline residue at position 3 of the β-turn. The observed structure supports the view that Aib residues initiate the formation of type III β-turn conformations. The pyrrolidine ring is puckered in C^γ-exo fashion.     

Sequential polypeptides containing arginine as histone models: synthesis and conformational studies

The sequential polypeptides (L -Arg-X-Gly)_n, where X represents amino acid residues Ala, Val, and Leu, were prepared as models of arginine-rich histones to be used in studying their structure and their interactions with DNA. The polymerization was carried out on the pentachlorophenyl active esters of the appropriate tripeptides, while the toluene-4-sulfonyl group was used for protecting the arginine guanido group. CD was employed to investigate the conformation of (L -Arg-X-Gly)_n polymers in aqueous solutions, at different pH, as well as in trifluoroenthanol and hexafluoroisopropyl alcohol solutions. In aqueous solutions (at pH 7 and 12) the prepared sequential polymers behaved as a random coil. The CD spectra in various trifluoroethanol–water or hexafluoroisopropyl alcohol–water mixtures indicated that the degree of helical conformation of the studied polytripeptides increased in the order of Ala → Val → Leu. The opposite was true for the β-structure. Characteristics of β-turn are excluded from the poly(L -Arg-L -Leu-Gly), which assumed the most pronounced helical conformation. The poly(L -Arg-L -Val-Gly) exerts a significant preference to the β-turn structure compared to that of poly(L -Arg-L -Ala-Gly). Thus the probability for helical, β-structure or β-turn conformations of the polymers was analyzed in relation to the bulkiness and length, and to the special features of the X-residue side chain (β-branching). We concluded that the prepared sequential arginine-containing polypeptides are plausible models for histone fractions, f₃ and f₂α₁.     

Stereochemistry of peptides containing 1-aminocyclopentanecarboxylic acid (Acc5): Solution and solid-state conformations of Boc-Acc5-Acc5-NHMe

The conformational analysis of a protected homodipeptide of 1-aminocyclopentanecarboxylic acid (Acc⁵) has been carried out. ¹H-nmr studies establish a β-turn conformation for Boc-Acc⁵-Acc⁵-NHMe in chloroform and dimethylsulfoxide solutions involving the methylamide NH in an intramolecular hydrogen bond. Supportive evidence for the formation of an intramolecular hydrogen bond is obtained from ir studies. X-ray diffraction studies reveal a type III β-turn conformation in the solid state stabilized by a 4 → 1 hydrogen bond between the Boc CO and methylamide NH groups. The ?,ψ values for both Acc⁵ residues are close to those expected for an ideal 3₁₀-helical conformation (?? ± 60°, ψ～ ±30°).     

Conformational variability of Gly-Gly segments in peptides: A comparison of the crystal structures of an acyclic pentapeptide and an octapeptide

The crystal structure of an acyclic pentapeptide, Boc-Gly-Gly-Leu-Aib-Val-OMe, reveals an extended conformation for the Gly-Gly segment, in contrast to the helical conformation determined earlier in the octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aib-Val-OMe [I. L. Karle, A. Banerjee, S. Bhattacharjya, and P. Balaram [1996] Biopolymers, Vol. 38, pp. 515–526). The pentapeptide crystallizes in space group P2₁ with one molecule in the asymmetric unit. The cell parameters are: a = 10.979(2) Å, b = 9.625(2) Å, c = 14.141(2) Å, and β = 96.93(1)°, R = 6.7% for 2501 reflections (I > 3σ(I)). The Gly-Gly segment is extended (ϕ₁ = −92°, ψ₁ = −133°, ϕ₂ = 140°, ψ₂ = 170°), while the Leu-Aib segment adopts a type II β-turn conformation (ϕ₃ = −61°, ψ₃ = 130°, ϕ₄ = 71°, ψ₄ = 6°). The observed conformation for the pentapeptide permits rationalization of a structural transition observed for the octapeptide in solution. An analysis of Gly-Gly segments in peptide crystal structures shows a preference for either β-turn or extended conformations. © 1997 John Wiley & Sons, Inc.     

Solid state and solution conformations of a helical peptide with a central gly-gly segment

The influence of amino acids with contrasting conformational tendencies on the stereochemistry of oligopeptides has been investigated using an octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aib-Val-OMe, which contains two helix-promoting Aib residues and a central helix-destabilizing Gly-Gly segment. Single crystal x-ray diffraction studies reveal that a 3 ₁₀-helix is formed up to the penultimate Aib residue, at which point there is a helix reversal in the backbone, reminiscent of a C-terminal 6 → I hydrogen bond. The curious feature in the crystal is the solvation of the possible 6 → 1 bond by a CH₃OH molecule, where the OH is inserted between O(3) and N(8) and participates in hydrogen bonds with both. The cell parameters are as follows: space group P2₁2₁2₁, a = 10.649(4) Å, b = 15.694(5) Å, c = 30.181(8) Å, R = 6.7% for 3427 data (| F₀| > 3σF) observed to 0.9 Å. Nuclear magnetic resonance studies in CDCl₃ using NH group solvent accessibility and nuclear Overhauser effects as probes are consistent with a 3 ₁₀-helical conformation. In contrast, in (CD₃)₂SO, unfolding of the central segment results in a multiple β-turn structure, with β-turn conformations populated at residues 1–2, 3–4, and 6–7. CD studies in methanol-2,2,2-trifluoroethanol (TFE) mixtures also provide evidence for a solvent-dependent structural transition. Helical conformations are populated in TFE, while type II β-turn structures are favored in methanol. © 1996 John Wiley & Sons, Inc.     

A search for the ideal type I β-turn

In 1968 C. Venkatachalam (Biopolymers, Vol. 6, pp. 1425–1436) predicted the ideal forms of β-turns (type I, type II, etc.) based entirely on theoretical calculations. Subsequently, over a thousand x-ray structures of different globular proteins have been analyzed, with results suggesting that the most important form among the hairpin conformers is the type I β-turn. For the latter type of hairpin conformation, the original computations had predicted ϕ_i+1 = −60°, ψ_i+1 = −30°, ϕ_i+2 = −90°, and ψ_i+2 = 0° as backbone torsion angle values, and these have been used from that time as reference values for the identification of the type I β-turn. However, it has never been clarified whether these “ideal” backbone torsion angle values exist in real structures, or whether these torsion angles are only “theoretical values.” Using the most recent release of the Protein Data Bank (1994), a survey has been made to assign amino acid pairs that approach the ideal form of the type I β-turn. The analysis resulted in four sequences where the deviation from ideal values for any main-chain torsion angles was less than 2°. In order to determine whether such a backbone fold is possible only in proteins owing to fortuitous cooperation of different folding effects, or whether it occurs even in short peptides, various attempts have been made to design the optimal amino acid sequence. Such a peptide model compound adopting precisely the predicted torsion angle values [ϕ_i+1 = −60°, ψ_i+1 = −30°, ϕ_i+2 = −90°, and ψ_i+2 = 0°] could provide valuable information. The solid state conformation of cyclo[(δ) Ava-Gly-Pro-Thr (O¹Bu)-Gly] reported herein, incorporating the -Pro-Thr- subunit, yields values suggesting that the “ideal” type I β-turn is even possible for a peptide where there are no major environmental effects present. © 1996 John Wiley & Sons, Inc.     

A comparative NMR and molecular dynamics study of the conformations of bradykinin B1 and B2, B2, and B1-specific receptor antagonists B-9430, B-9436, and B-9858

Extensive proton magnetic resonance experiments were carried out on three bradykinin peptide antagonists B-9430, B-9436, and B-9858 in aqueous solutions as well as in sodium dodecylsulphate micelles (B-9430 and B-9436) and CD₃OH/H₂O (60%/40%) mixtures for B-9858. All three peptides showed no observable secondary structure in aqueous solution. However, in their respective structure-inducing solvents, B-9430 (B₁ and B₂ receptor antagonist) and B-9436 (a B₂ receptor antagonist) exhibit a type II β-turn involving residues 2–5, and B-9430 also exhibits a type II′ β-turn involving residues 6–9 (in sodium dodecylsulfate micellar solutions), whereas B-9858, a B₁-specific receptor antagonist, exhibits only a type II β-turn involving residues 2–5 (in CD₃OH/H₂O solutions). Simulated annealing calculations on B-9858 confirm the experimental conclusions based on the nmr data. In addition, simulated annealing of the (2S, 3aS, 7aS)-octahydroindole-2-carboxylic acid (Oic residue), which is present in two of the three decapeptides studied, show that the one-chair conformation of the six-membered ring predominates, in agreement with the experimental data. The activities of these peptides are compared with their secondary structures and the specific receptor activity appears to depend on the presence of specific amino acid residues, such as N-(2-indanyl)glycine (Nig) and D[α-(2-indanyl)glycine] (D-Igl) as well as on elements of secondary structure. © 1997 John Wiley & Sons, Inc. Biopoly 42: 521–535, 1997     

Modified chemotactic peptides: Synthesis,conformation, and activity of HCO-Thp-Ac6c-Phe-OMe

HCO-Thp-Ac₆c-Phe-OMe (3) has been synthesized as a new analogue of the prototypical chemotactic agent HCO-Met-Leu-Phe-OMe (fMLP-OMe). Compound 3 contains 4-aminotetrahydrothiopyran-4-carboxylic acid (Thp) and 1-aminocyclohexane-1-carboxylic acid (Ac₆c) as achiral, conformationally restricted mimics of Met and Leu, respectively. In the crystal, the formyltripeptide adopts an helical conformation at the Thp and Ac₆c residues, of the type α_R and α_L, respectively, whereas the C-terminal phenylalanine is quasi-extended. A system of two consecutive γ-turns, centered at the first two residues, better explains the nmr data as compared with an alternative β-turn structure. The conformation of the new analogue 3 is compared with those of two related peptides containing Thp as N-terminal residue. The biological activity of 3 has been determined on human neutrophils and compared to that of the previously studied model [Ac₆c²] fMLP-OMe. While the above analogue is highly active in the superoxide anion production, the new tripeptide 3 is practically unable to elicit any of the tested biological activities. © 1996 John Wiley & Sons, Inc.     

Bioactive peptides: Conformational studies of [TYR4] cyclolinopeptide A

The solid state conformational analysis of [Tyr⁴] cyclolinopeptide A has been carried out by x-ray diffraction studies. The crystal structure of the monoclinic form, grown from a dioxane-water mixture [a = 9.849 (5) Å, b = 20.752 (4) Å, c = 16.728 (5) Å, β = 98.83 (3)°, space group P2₁, Z = 2], shows the presence of five intramolecular N-H? O?C hydrogen bonds, with formation of one C₁₇ ring structure, one α-turn (C₁₃), one inverse γ-turn (C₇), and two β-turns (C₁₀, one of type III and one of type 1). The Pro¹-Pro² peptide unit is cis (ω = 5°) all others are trans. The structure is almost superimposable with that of cyclolinopeptide A. The rms deviation for the atoms of the backbones is on the average 0.33 Å. © 1995 John Wiley & Sons, Inc.     

Peptides containing the sulfonamide junction: Synthesis,structure, and conformation of Z-Tau-Pro-Phe-NHiPr

The taurine (Tau) containing tripeptide derivative Z-Tau-Pro-Phe-NHiPr (1) has been synthesized as suitable sulfonamido-pseudopeptide model to investigate formation and conformational properties of folded secondary structures stabilized by intramolecular H bonds directly involving the sulfonamide junction. In the crystal the pseudopeptide 1 adopts a type I β-turn with the Pro and Phe residues located at the (i + 1) and (i + 2) corner positions, respectively. The turn is stabilized by a 4 → 1 H bond engaging one of the SO₂ oxygen atoms and the isopropylamide NH. In CDCl₃ solution the β-turn folding is accompanied by a γ-turn centered at the Pro and involving a 3 → 1 H bond between the SO₂ and the Phe NH. A comparison of the structural and conformational properties found in 1 with those of the already known sulfonamido-pseudopeptides, with particular reference to the models containing the Tau-Pro junction, is also reported. © 1997 John Wiley & Sons, Inc. Biopoly 41: 555–567, 1997.     

Structural versatility of peptides from Cα, α-disubstituted glycines: Crystal-state conformational analysis of homopeptides from Cα-methyl,Cα-benzylglycine [(αMe)Phe]n

The molecular and crystal structures of one derivative and three homopeptides (from the di-to the tetrapeptide level) of the chiral, C^{α, α}-disubstituted glycine C^α-methyl, C^α-benzylglycine [(αMe)Phe], have been determined by x-ray diffraction. The derivative is mClAc-D -(αMe)Phe-OH, and the peptides are pBrBz-[D -(αMe)Phe]₂-NHMe, pBrBz-[D -(αMe)Phe]₃-OH hemihydrate, and pBrBz-[D -(αMe)Phe]₄-OtBu sesquihydrate. All (αMe)Phe residues prefer ?,ψ torsion angles in the helical region of the conformational map. The dipeptide methylamide and the tripeptide carboxylic acid adopt a β-turn conformation with a 1 ← 4 C?O…?H? N intramolecular H bond. The structure of the tripeptide carboxylic acid is further stabilized by a 1 ← 4 C?O…?H? O intramolecular H bond, forming an “oxy-analogue” of a β-turn. The tetrapeptide ester is folded in a regular (incipient) 3₁₀-helix. In general, the relationship between (αMe)Phe chirality and helix screw sense is opposite to that exhibited by protein amino acids. A comparison is made with the conclusions extracted from published work on homopeptides from other C^α-methylated α-amino acids. © 1993 John Wiley & Sons, Inc.     

Synthesis,conformation, and activity of HCO-Met-ΔZ Leu-Phe-Ome,an active analogue of chemotactic N-formyltripeptides

In order to induce a β-turn conformation into the chemotactic linear tripeptide N-formyl-L -methionyl-L -leucyl-L -phenylalanine (fMLP), the new analogue N-formyl-L -methionyl-Δ^Zleucyl-L -phenylalanine methyl ester [ Δ^ZLeu]²f MLP-OMe ( 1 ) has been synthesized. The conformational and biochemical consequences of this chemical modification have been determined. Analogue 1 has been synthesized by using N-carboxy-(Z)-α,β-didehydroleucine anhydride as key compound to introduce the unsaturated residue at the central position of the tripeptide 1 . The x-ray analysis shows that 1 adopts in the crystal a type II β-turn conformation in which the new residue occupies the (i + 2) position, and an intramolecular H bond is formed between the formylic oxygen and the Phe NH. ¹H-nmr analysis based on nuclear Overhauser effect measurements suggests that the same folded conformation is preferred in CDCl₃ solution; this finding is also supported by molecular dynamics simulation. The biological activity of 1 has been determined on human neutrophils (polymorphonuclear leukocytes) and compared to that shown by f MLP-OMe. Chemotactic activity, granule enzyme release, and superoxide anion production have been determined. Analogue 1 is practically inactive as chemoattractant, highly active in the superoxide generation, and similar to the parent in the lysozyme release. The conformational restriction imposed on the backbone by the presence of the unsaturated residue is discussed in relation with the observed bioselectivity. © 1993 John Wiley & Sons, Inc.     

Raman study of crystalline peptides containing beta turns

The Raman spectra of crystalline H-ProLeuGlyNH₂ which has a type II β turn, crystalline S-benzylCysProLeuGlyNH₂ which has a type I β-turn, and crystalline gramicidin S which has two β turns and β-sheet structure in its conformation, were investigated. The amide I and amide III bands of the peptides with β turns were generally different from those which are diagnostic for α-helix and β-sheet conformations. The patterns of the amide I and amide III bands, when examined together, indicate that Raman spectra can provide diagnostic evidence for β-turn structure in peptides.     

Conformational interconversions in peptide β-turns: Discrimination between enantiomeric conformations by chiral perturbation

The crystal structure of the model tripeptide Boc-Aib-Gly-Leu-OMe ( 1 ) reveals two independent molecules in the asymmetric unit that adopt “enantiomeric” type I and type I′ β-turn conformations with the Aib and Gly residues occupying the corner (i + 1 and i + 2) positions. ¹³C cross polarization and magic angle sample spinning spectra in the solid state also support the coexistence of two conformational species. ¹³C-nmr in CDCl₃ establishes the presence of a single species or rapid exchange between conformations. 400 MHz ¹H-nmr provides evidence for conformational exchange involving a major and minor species, with β-turn conformations supported by the low solvent exposure of Leu(3) NH and the observation of N_iH ↔ N_i+1H nuclear Overhauser effects. CD bands in the region 190–230 nm are positive, supporting a major population of type I′ β-turns. The isomeric peptide, Boc-Gly-Leu-Aib-OMe ( 2 ), adopts an “open” type II′ β-turn conformation in crystals. Solid state and solution nmr support population of a single conformational species. Chiral perturbation introduced outside the folded region of peptides may provide a means of modulating screw sense in achiral sequences. © 1998 John Wiley & Sons, Inc. Biopoly 45: 191–202, 1998     

A type II β-turn in a flexible peptide: Proton assignment and conformational analysis of the α-factor from saccharomyces cerevisiae in solution

Two-dimensional ¹H-nmr spectra of the α-mating factor [in dimethyl sulfoxide-d₆ (DMSO) and in water] and several dodecapeptide analogues (in DMSO) were obtained. Homonuclear correlated spectroscopy resulted in the complete and unequivocal assignment of all backbone and side-chain resonances of the peptides. The solution conformation of the pheromones was probed using two-dimensional (2D) nuclear Overhauser effect spectroscopy (NOESY) and rotating frame nuclear Overhauer effect spectroscopy (ROESY). The 2D NOE results, and results of complementary one-dimensional experiments, suggest that a type II β-turn is assumed by the central portion of active pheromones in both DMSO and water. Inactive analogues of the α-factor do not exhibit this structural feature. Except for this one β-turn, the nmr parameters for α-factor are indicative of a conformationally flexible molecule in both solvents. This conclusion is in contrast to that of other researchers who have proposed a highly structured conformation of α-factor in aqueous solution.