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  • 1
    Electronic Resource
    Electronic Resource
    Helix aggregation in peptide crystals: Occurrence of either all parallel or antiparallel packing motifs for α-helices in polymorphs of Boc-Aib-Ala-Leu-Ala-Leu-Aib-Leu-Ala-Leu-Aib-OMe (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1835-1845 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three crystalline polymorphs of the helical decapeptide, Boc-Aib-Ala-Leu-Ala-Leu-Aib-Leu-Ala-Leu-Aib-OMe, have been obtained. Antiparallel helix aggregation is observed in crystals grown from methanol (A), while completely parallel packing is observed in crystals from isopropanol (B) or an ethylene glycol-ethanol mixture (C). Crystals B and C are very similar in molecular conformation and packing. The packing motifs in crystals A and B consist of rows of parallel molecules, with an almost identical arrangement in both crystals. In crystal A, adjacent rows assemble with helix axes pointed in oppsite directions, whereas in crystal B all rows assemble with helix axes pointed in the same direction. Electrostatic interactions between helix dipoles do not appear to be a major determinant of packing modes. The structures also do not provide a ready rationalization of packing preferences in terms of side-chain interactions or solvation. The α-helix of the peptide in crystal A has seven 5 → 1 hydrogen bonds; the helix in crystal B is a mixed 310/α-helix. The crystal parameters are as follows. Crystal A: C51H92N10O13·CH3OH, space group P21 with a = 10.498(1) Å, b = 18.189(3) Å, c = 16.475(3) Å, β = 99.28(1)°, Z = 2, R = 9.6% for 1860 data. Crystal B: C51H92N10O13·C3H7OH, space group P21 with a = 10.534(1) Å, b = 28.571(4) Å, c = 11.055(2) Å, β = 95.74(1)°, Z = 2, R = 6.5% for 3251 data. Crystal C: C51H92N10O13·C2H5OH, space group P21, with a = 10.450(1) Å, b = 28.442(5) Å, c = 11.020(2) Å, β = 95.44(1)°, Z = 2, R = 14.8% (isotropic) for 1948 data.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360291414
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  • 2
    Electronic Resource
    Electronic Resource
    Synthetic peptide helices in crystals: Structure and antiparallel and skewed packing motifs for α-helices in two isomeric decapeptides (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 719-731 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The isomeric decapeptides Boc-Aib-Ala-Leu-Ala-Aib-Aib-Leu-Ala-Leu-Aib-OMe (II) and Boc-Aib-Ala-Aib-Ala-Leu-Ala-Leu-Aib-Leu-Aib-OMe (III), are predominantly a-helical with little effect on the conformation with interchange of Aib/Ala residues or Aib/Leu residues. The packing motif of helices in crystal II is antiparallel, whereas the helices pack in a skewed fashion in crystal III, with a 40° angle between neighboring helix axes. Crystal III contains a water molecule in a hydrophobic hole that forms hydrogen bonds with two carbonyl oxygens that also participate in 5 → 1 type hydrogen bonds. Values for helical torsional angles φ and ψ assume a much wider range than anticipated. Crystal II: C49H88N10O13, space group P21 with a = 16.625(2) Å, b = 9.811(5) Å, c = 18.412(3) Å, β = 99.79(1)°, Z = 2, R = 5.7% for 4338 data with |F0 | 〉 3σ(F). Crystal III: C49H88N10O13. 1/2H2O, space group P21, with a = 11.072(2) Å, b = 34.663(5) Å, c = 16.446(3) Å, β = 107.85(1) °, Z = 4, R = 8.3% for 6087 data with |F0| 〉 3σ(F).
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360300707
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  • 3
    Electronic Resource
    Electronic Resource
    Crystal state conformation of three model monomer units for the β-bend ribbon structure (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1669-1676 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular and crystal structures of three compounds, representing the repeating units of the β-bend ribbon (an approximate 310-helix, with an intramolecular hydrogen-bonding donor every two residues), have been determined by x-ray diffraction. They are Boc-Aib-Hib-NHBzl, Z-Aib-Hib-NHBzl, and Z-L-Hyp-Aib-NHMe (Aib, α-aminoisobutyric acid; Bzl, benzyl; Boc, t-butyloxycarbonyl; Hyp, hydroxyproline Hib, α-hydroxyisobutyric acid; Z, benzyloxycarbonyl). The two former compounds are folded in a β-bend conformation: type III (III′) for Boc-Aib-Hib-NHBzl, while type II (II′) for the Z analogue. Conversely, the structure of Z-L-Hyp-Aib-NHMe, although not far from a type II β-bend, is partially open.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311402
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  • 4
    Electronic Resource
    Electronic Resource
    Peptide design: Influence of a guest Aib-Pro segment on the stereochemistry of an Oligo-Val sequence - solution conformations and crystal structure of Boc-(Val)2-Aib-Pro-(Val)3-OMe (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1433-1442 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The peptide Boc-Val-Val-Aib-Pro-Val-Val-Val-OMe has been synthesized to investigate the effect of introduction of a strong β-turn promoting guest segment into an oligopeptide with a tendency to form extended structures. 1H-nmr studies in solution using analysis of NH group solvent accessibility and nuclear Overhauser effects suggest an appreciable solvent dependence of conformations. In chloroform a 310-helical structure is favored while in dimethylsulfoxide an Aib-Pro β-turn with extended arms on either side is suggested. In the crystal, the backbone forms a somewhat distorted 310-helix despite the presence of a Pro residue in the middle. Among the four possible intrahelical hydrogen bonds three are of the 4 → 1 type and one 5 → 1. Head-to-tail NH⃛O=C hydrogen bonds link the helical molecules into continuous columns. The space group is P212121 with a = 11.320(2), b = 19.889(3), and c = 21.247(3) Å.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360291010
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  • 5
    Electronic Resource
    Electronic Resource
    Unfolding of an α-helix in peptide crystals by solvation: Conformational fragility in a heptapeptide (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 827-837 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of the peptide Boc-Val-Ala-Leu-Aib-Val-Ala-Leu-OMe has been determined in crystals obtained from a dimethylsulfoxide-isopropanol mixture. Crystal parameters are as follows: C38H69N7O10 · H2O · 2C3H7OH, space group P21, a = 10.350 (2) Å, b = 26.084 (4) Å, c = 10.395(2) Å, β = 96.87(12), Z = 2, R = 8.7% for 2686 reflections observed 〉 3.0 σ (F). A single 5 → 1 hydrogen bond is observed at the N-terminus, while two 4 → 1 hydrogen bonds characteristic of a 310-helix are seen in the central segment. The C-terminus residues, Ala(6) and Leu(7) are expended, while Val(5) is considerably distorted from a helical conformation. Two isopropanol molecules make hydrogen bonds to the C-terminal segment, while a water molecule interacts with the N-terminus. The structure is in contrast to that obtained for the same peptide in crystals from methanol-water [ I. L. Karle, J. L. Flippen-Anderson, K. Uma, and P. Balaram (1990) Proteins: Structure, Function and Genetics, Vol. 7, pp. 62-73] in which two independent molecules reveal an almost perfect α-helix and a helix penetrated by a water molecule. A comparison of the three structures provides a snapshot of the progressive effects of solvation leading to helix unwinding. The fragility of the heptapeptide helix in solution is demonstrated by nmr studies in CDC13 and (CD3)2SO. A helical conformation is supported in the apolar solvent CDCl3, whereas almost complete unfolding is observed in the strongly solvating medium (CD3)2SO. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330511
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  • 6
    Electronic Resource
    Electronic Resource
    Conformation of the flexible bent helix of Leu1-zervamicin in crystal C and a possible gating action for ion passage (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 721-735 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The membrane channel-forming polypeptide, Leu1-zervamicin, Ac-Leu-Ile-Gln-Iva-Ile5-Thr-Aib-Leu-Aib-Hyp10-Gln-Aib-Hyp-Aib-Pro15-Phol (Aib: α-aminoisobutyric acid; Iva: isovaline; Hyp: 4-hydroxyproline; Phol: phenylalininol) has been analyzed by x-ray diffraction in a third crystal form. Although the bent helix is quite similar to the conformations found in crystals A and B, the amount of bending is more severe with a bending angle ≈ 47°. The water channel formed by the convex polar faces of neighboring helices is larger at the mouth than in crystals A and B, and the water sites have become disordered. The channel is interrupted in the middle by a hydrogen bond between the OH of Hyp (10) and the NH2 of the Gln (11) of a neighboring molecule. The side chain of Gln (11) is wrapped around the helix backbone in an unusual fashion in order that it can augment the polar side of the helix. In the present crystal C there appears to be an additional conformation for the Gln (11) side chain (with ≈ 20% occupancy) that opens the channel for possible ion passage. Structure parameters for C85H140N18O22 · xH2O · C2H5OH are space group P212121, a = 10.337(2) Å, b = 28.387(7) Å, c = 39.864(11) Å, Z = 4, agreement factor R = 12.99% for 3250 data observed 〉 3σ(F), resolution = 1.2 Å. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340605
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  • 7
    Electronic Resource
    Electronic Resource
    Stereochemical constraints in peptide design: Analysis of the influence of a disulfide bridge and an α-aminoisobutyryl residue on the conformation of a hexapeptide (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 865-871 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The competing effects of a disulfide bridge and an α-aminoisobutyryl residue (Aib) in determining the conformation of a hexapeptide have been investigated, by comparing the cyclic disulfide (1) and the acylic peptide Boc-Cys(SBzl)-Val-Aib-Ala-Leu-Cys(SBzl)-NHMe (2). Previously published nmr and crystallographic studies [R. Kishore, S. Raghothama, and P. Balaram (1987) Biopolymers, Vol. 26, pp. 873-891; I. L. Karle, R. Kishore, S. Raghothama, & P. Balaram, (1988) Journal of the American Chemical Society Vol. 110, pp. 1958-1963] have established an antiparallel β-hairpin structure for 1 with a central Aib-Ala β-turn. A comparison of nmr data for 1 and 2 in chloroform and dimethylsulfoxide reveals that the acyclic peptide is conformationally labile. Evidence for a 310-helical conformation in CDCl3 is obtained from sensitivity of NH chemical shifts to temperature and solvent perturbation and low JHNCαH values. Studies in solvent mixtures establish a conformational transition on going from CDCl3 to (CD3)2SO. The changes in NH nmr parameters, together with the observation of several interresidue Ciα H-Ni + 1H nuclear Overhauser effects support a conformation having a central β-turn with extended arms in (CD3)2SO. A single Aib residue appears to stabilize a helix in apolar solvents, for the acyclic hexapeptide, while the disulfide bridge serves to lock the β-hairpin conformation. © 1993 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330602
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  • 8
    Electronic Resource
    Electronic Resource
    Accommodation of a D-Phe residue into a right-handed 310-helix: Structure of Boc-D-Phe-(Aib)4-Gly-L-Leu-(Aib)2-Ome, an analogue of the amino terminal segment of antiamoebins and emerimicins (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 401-407 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of the nonapeptide Boc-D-Phe-Aib-Aib-Aib-Aib-Gly-Leu-Aib-AibOMe (I), which is an analogue of the N-terminal sequence of antiamoebins and emerimicins, establishes a completely 310-helical conformation with seven successive intramolecular 4 → 1 hydrogen bonds. The average, φ, ψ values for residues 1-8 are -59° and -32°, respectively. Crystal parameters are C47H77N9O12, space group P1, a = 10.636(4) Å, b = 11.239(4) Å, c = 12.227(6) Å, α = 101.17(4)°, β = 97.22(4)°, γ = 89.80(3)°, Z = 1, R = 5.95% for 3018 data with |F0| 〉 3α(F), resolution 0.93 Å. The use of the torsion angle κ = C(i - 1)N(i)Cα(i)Cβ(i), where κ = 68° for D-Phe and κ = 164° for L-Leu, confirms the opposite configurations of these residues. The φ, ψ values of -62° and -32° at D-Phe are unusual, since this region is characteristic of residues with L configurations. Peptide I possesses only two chiral residues of opposing configuration. The observed right-handed 310-helical structure suggests that helix sense has probably been determined by the stereo-chemical preferences of the Leu residue. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330308
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