摘要:

AbstractIn our attempts to design crystalline α‐helical peptides, we synthesized and crystallized GAI (C11H21N3O4) in two crystal forms, GAI1 and GAI2. Form 1 (GAI1) Gly‐L‐Ala‐L‐Ile (C11H21N3O4· 3H2O) crystals are monoclinic, space group P21witha= 8.171(2),b= 6.072(4),c= 16.443(4) Å, β = 101.24(2)°,V= 800 Å3,Dc= 1.300 g cm‐3andZ= 2,R= 0.081 for 482 reflections. Form 2 (GAI2) Gly‐L‐Ala‐L‐Ile (C11H21N3O4· ½H2O) is triclinic, space group P1 witha= 5.830 (1),b= 8.832 (2),c= 15.008(2) Å, α = 102.88 (1), β = 101.16(2), γ = 70.72(2)°,V= 705 Å3,Z= 2,Dc= 1.264 g cm−3,R= 0.04 for 2582 reflections. GAI1 is isomorphous with GAV and forms a helix, whereas GAI2 does not. In GAI1, the tripeptide molecule is held in a near helical conformation by a water molecule that bridges the NH+3and COO−groups, and acts as the fourth residue needed to complete the turn by forming two hydrogen bonds. Two other water molecules form intermolecular hydrogen bonds in stabilizing the helical structure so that the end result is a column of molecules that looks like an incipient a‐helix. GAI2 imitates a cyclic peptide and traps a water molecule. The conformation angles χ11and χ12for the side chain are ( –63.7°, 171.1°) for the helical GAI1, and (–65.1°, 58.6°) and (–65.0°, 58.9°) for the two independent nonhelical molecules in GAI2; in GAI1, both the C, atoms point away from the helix, whereas in GAI2 the Cγatom with theg+conformation points inward to the helix and causes sterical interaction with atoms in the adjacent peptide plane. From these results, it is clear that the helix‐forming tendencies of amino acids correlate with the restrictions of side‐chain rotamer conformations. Both the peptide units in GAI1 aretransand show significant deviation from planarity [ω1= –168(1)°; ω2= –171(1)°] whereas both the peptide units in both the molecules A and B in GAI2 do not show significant deviation from planarity [ω1= 179.3(3)°; ω2= –179.3(3)° for molecule A and ω1= 179.5(3)°; omega;2= –179.4 (3) ° for molecule B], indicating that

ISSN:0006-3525    

DOI:10.1002/bip.360320202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe importance of side‐chain charge interactions in the formation of β‐turns was studied. Sixteen protected NAc‐tetrapeptide amides were studied, namely the variants of DEKS: NEKS, EEKS, DDKS, DQKS, NQKS, DERS, NERS, EERS, DDRS, NDRS, DQRS, and DKES. Three tetrapeptides—NPDM, NSDM, and NDDS—were also studied as they have a high probability of forming β‐turns, based on statistical predictions. The results indicate that a small proportion of type I β‐turn exists in solutions of DEKS and DERS in methanol/ water (60/40), while NEKS has an even smaller population of this turn. The other tetrapeptides are present in solution only in the extended conformation. These results clearly show the importance of the salt bridge between the side chains of K2and E3or R2and E3, as well as the importance of the charge on the side chain of the first residue in stabilizing the β‐turn. The relevance of statistical predictions for β‐turns in short

ISSN:0006-3525    

DOI:10.1002/bip.360320203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractIn order to investigate the conformational variation of ascidiacyclamide, a cytotoxic cyclic peptide from marine tunicateAscidian, single crystals were prepared from ethanol and aqueous ethanol solutions as its free form (crystal I) and H2O/0.5 C2H5OH solvate (crystal II), respectively, and were determined by the x‐ray diffraction method. Crystal I showed a pseudoC2‐symmetric saddle‐shaped rectangular conformation. Similar conformations were also observed in crystal II, where there were two crystallographically independentC2‐symmetric molecules (named Mol‐A and ‐B) per asymmetric unit. Mol‐A and ‐B included H2O and H2O/C2H5OH solvents within their ring structures, respectively. These water and ethanol molecules were located on the crystallographic dyad axes, and were stabilized by the van der Waals contacts (including hydrogen bonds) with the polar‐ring N atoms and nonpolarD‐Val side‐chain atoms. The conformational characteristics of ascidiacyclamide and its fluctuation/variation were discussed based on the present and previously r

ISSN:0006-3525    

DOI:10.1002/bip.360320204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractBase‐stacking and phosphate‐phosphate interactions in B‐DNA are studied using the finite difference Poisson–Boltzmann equation. Interaction energies and dielectric constants are calculated and compared to the predictions of simple dielectric models. No extant simple dielectric model adequately describes phosphate–phosphate interactions. Electrostatic effects contribute negligibly to the sequence and conformational dependence of base‐stacking interactions. Electrostatic base‐stacking interactions can be adequately modeled using the Hingerty screening function. The repulsive and dispersive Lennard–Jones interactions dominate the dependence of the stacking interactions on roll, tilt, twist, and propeller. The Lennard–Jones stacking energy in ideal B‐DNA is found to be essentially inde

ISSN:0006-3525    

DOI:10.1002/bip.360320205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe conformational behavior of the synthetic peptide, Boc‐Gly‐Val‐Gly‐Gly‐Leu‐OMe, containing the X‐Gly‐Gly and Gly‐Gly‐X (X = Val or Leu) repeating sequences and constituting a fragment of elastin was investigated by molecular mechanics and molecular dynamics (MD) simulation. The results suggest that, irrespective of the approximations used, the molecule shows a manifold of low energy conformations characterized by γ‐turns and type II β‐turns. Furthermore, MD simulations point out a conformational floppiness due to very low barriers between different conformations. Experimental CD measurements in a virtually apolar medium (dioxane − ε = 2.209), which better mimics the vacuum conditions of the simulation, support the theoretical results. The general emerging picture, indicating the molecule as characterized by a combination of flexibility with conformational preferences, is in agreement with previous experimental findings and enriches of new aspects the description of the microscopic behavior of this molecule suggesting more detailed int

ISSN:0006-3525    

DOI:10.1002/bip.360320206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractIn the present paper we describe the synthesis, purification, single crystal x‐ray analysis, and solution conformational characterization of the cyclic tetrapeptidecyclo‐ (L‐Pro‐γ‐Ala‐L‐Pro‐γ‐Ala). This peptide was synthesized by classical solution methods and the cyclization of the free tetrapeptide was accomplished in good yields in diluted methylene chloride solution using N, N‐dicyclohexyl‐carbodiimide (DCCI). The compound crystallizes in the orthorombic space group P212121from ethyl acetate. All peptide bonds aretrans. The molecular conformation is stabilized by two intramolecular hydrogen bonds between the CO and NH groups of the two β‐alanine residues. These hydrogen bonds take part in a C7structure in which both proline residues occupy the 2 position of an inverse γ‐turn. The two β‐alanine residues have a typical folded conformation (around the Cα‐Cβ bond) observed in other cyclic peptides containing this residue. A detailed1H‐nmr analysis in CD3CN solution has been carried out. The molecule assumes a twofold symmetry in solution with a molecular conformation consistent

ISSN:0006-3525    

DOI:10.1002/bip.360320207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractHelix formation in (Lys)n· HClO4and poly(Nε, Nε, Nε–trimethyl‐L‐lysine) · HClO4[(LysMe3)n· HClO4] is dependent on peptide concentration and on molecular weight. For (LysMe3)n· HClO4of degree of polymerization (DP) 2510 the midpoint of the coil‐to‐helix transition is 2 mMand for DP of 190 it is 5 mM. For (Lys)n· HC1O4the peptide concentration for half‐helix is 30–60 times as high, and is only weakly dependent, if at all, on molecular weight. Helix formation is an intermolecular process. The use of methylated (Lys)nas the perchlorate permits study of the intermolecular coil‐helix transition at low concentration, instead of the high concentration (ca. 1–2M) required for (Lys)n· HBr. At constant peptide concentration helix content increases with added NaClO4. The higher the peptide concentration, the less NaClO

ISSN:0006-3525    

DOI:10.1002/bip.360320208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe 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 e

ISSN:0006-3525    

DOI:10.1002/bip.360320209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360320201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY