摘要:

AbstractTo better understand the structural basis of the biological activity of the neuropeptide substance P SP; (Arg‐Pro‐Lys‐Pro‐Gln‐Gln‐Phe‐Phe‐Gly‐Leu‐Met‐NH2), two‐dimensional nmr spectroscopy experiments and simulated annealing calculations were used to investigate the conformation adopted in the presence of the membrane model system sodium dodecyl sulfate. It was determined that SP in the presence of SDS micelles undergoes a conformational equilibrium between an α‐ and a 310‐helix involving the midregion (Pro4‐Gln5‐Gln6‐Phe7‐Phe8) of the peptide. The C‐terminus adopts an extended conformation while the N‐terminus remains quite flexible. The conformation adopted by SP in the presence of SDS micelles yields a structure that is consistent with the model of a neurokinin‐1 selective ligand propos

ISSN:0006-3525    

DOI:10.1002/bip.360341102

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

年代:1994

数据来源: WILEY

摘要:

AbstractA single‐crystal x‐ray diffraction analysis of Boc‐L‐Ala‐D‐aIle‐L‐Ile‐OMe has been carried out. The analysis has shown (a) that the tripeptide molecules have in part an α‐extended conformation, the torsion angles of theL‐Ala andD‐aIle residues being φ1= −75.1° and ψ1= −25.8° and φ2= 67.3° and ψ2= 44.1°, respectively, and (b) that the molecules are organized in rippled planes where they occur in relative antiparallel orientation linked together side by side by H bonds. This molecular organization of the tripeptide corresponds closely to that of an antiparallel α‐pleated sheet, and likely constitutes the first example of a structure of this kind for which a characterization at the atomic level has been achieved. A molecular dynamics study has shown that the molecular conformation of the tripeptide in the crystalline state is determined primarily by intermolecular in

ISSN:0006-3525    

DOI:10.1002/bip.360341103

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

年代:1994

数据来源: WILEY

摘要:

AbstractFlow linear dichroism measurements extended into the vacuum uv region yield inclinations for the base normal from the helix axis of 21° for dA and 40° for dT in the X‐form of poly (dAdT) · poly (dAdT). These inclination angles are similar to the B form of the synthetic polymer, but the axes around which the bases incline are different. Hydrogen‐bonded base pairs are consistent with the geometry for the standard B, C, D, and Z forms of natural DNA, but will not fit into the A form. Fourier transform ir spectra indicate that the X form has sugar pucker and phosphate geometry similar to B‐form DNA, and supports the dinucleotide repeat with two kinds of phosphates seen in earlier work, in analogy to Z‐form DNA. Clearly, X‐form DNA has a unique geometry. © 1994 John Wi

ISSN:0006-3525    

DOI:10.1002/bip.360341104

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

年代:1994

数据来源: WILEY

摘要:

AbstractNuclear Overhauser effect spectroscopy measurements on cellulose triacetate and on amylose triacetate with a mixing time of 500 ms, on the order ofT1, of acetyl protons, were performed to detect the specific through‐space interaction between acetyl groups arising from their helix structures in solution. For cellulose triacetate, cross peaks were detected in CDCl3between acetyl proton signals at 3 and 6 positions on an anhydroglucose unit. In DMSO‐d6, on the other hand, correlation peaks were observed not only between the 3 and 6 positions but also the 2 and 6 positions. For amylose triacetate, cross peaks were detected in CDCl3between the acetyl proton signals at the 2 and 6 positions. The through‐space interaction of acetyl groups in cellulose triacetate and in amylose triacetate in solution was then interpreted based on their three‐dimensional structures in solid state determined by x‐ray crystallography. © 1994 John Wiley

ISSN:0006-3525    

DOI:10.1002/bip.360341105

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe present an analysis of the response of native DNA solutions to well‐defined elongational flow fields. At low strain rates the DNA duplex behaves as an expanded coil. It shows a noncritical coil‐stretch transition, suggesting relatively little hysteresis of the relaxation time. On the other hand, the relaxation time is consistent with a nonfree draining coil. At higher strain rates we observe midpoint scission. This has been modeled very successfully as a thermomechanically activated process. Scission occurs at hydrolyzable weak linkages along the constituent strands. Complete scission of the DNA helix is, however, considerably less prevalent than would be expected given the low stability of the constituent strands. We speculate upon the molecular origin and biological consequences of this enhanced stability. © 1994 John Wiley&Sons,

ISSN:0006-3525    

DOI:10.1002/bip.360341106

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

年代:1994

数据来源: WILEY

摘要:

AbstractA quantitative estimate of the activation energy for grain growth has been obtained by analyzing ice recrystallization experiments from water and from solutions with small amounts (<1.0 μg/mL) of antifreeze glycoprotein (AFGP). Rates of grain growth are measured as changes of grain diameter in time, with the supercooled holding temperature aVid glycoprotein concentration as parameters. Arrhenius plots of these rates vs (1/T) yielded slopes proportional to the activation energies for the particular species. The values of activation energy are almost independent of solution concentration or the species of AFGP. Averaged activation energy value for the AFGP‐4 species isQg= (6.61 ± 1.02) × 105J/mole. The “less active” AFGP‐8 yielded an averageQg= (5.71 ± 2.39) × 105J/mole, quite similar to the AFGP‐4 species. The activation energy for recrystallization in a pure ice‐water system was estimated from two temperature points,T= −5.4 and −7.5°C. The best value is 2.39 × 105J/mole, nearly twice that obtained by M. N. Martino and N. E. Zaritsky [(1989)Cryobiology, Vol. 26, p. 138] in a recrystallization experiment using salt solution, but much smaller than the values derived from the AFGP solutions. Results further show that activation entropy is at least a factor of 2 larger for the AFGP species than that of pure ice‐water system under the same growth conditions. These results suggest significant roles, both energetically and entropically, for AFGP molecules in their ability to inhibit grain growth of ice. ©

ISSN:0006-3525    

DOI:10.1002/bip.360341107

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn the present paper we describe the synthesis, purification, single crystal x‐ray analysis, and solution structural characterization by nmr spectroscopy, combined with restrained molecular dynamic simulations, of the cyclic hexapeptidecyclo‐(Pro‐Phe‐β‐Ala‐Phe‐Phe‐β‐Ala). The peptide was synthesized by classical solution methods and the cyclization of the free hexapeptide was accomplished in good yields in diluted methylenechloride solution usingN,N‐dicyclohexyl‐carbodiimide. The compound crystallizes in the monoclinic space group P21from methanol/ethyl acetate. The molecule adopts in the solid state a conformation characterized bycisβ‐Ala6‐Pro1peptide bond. The α‐amino acid residues are at the corner positions of turned structures. The Pro1‐Phe2segment is incorporated in apseudotype I β‐turn, while Phe4‐Phe5is in a typical type I β‐turn. Assignment of all1H and13C resonances was achieved by homo‐ and heteronuclear two‐dimensional techniques in dimethylsulfoxide (DMSO) solutions. The conformational analysis was based on inter‐proton distances derived from rotating frame nuclear Overhauser effect spectroscopy spectra and homonuclear coupling constants. Restrained molecular dynamic simulation in vacuo was also performed to built refined molecular models. The molecule is present in DMSO solution as two slowly interconverting conformers, characterized by acis‐tranisomerism around the β‐Ala6‐Pro1peptide bond. This work confirms our expectations on the low propensity of β‐alanyl residues to be positioned at the

ISSN:0006-3525    

DOI:10.1002/bip.360341108

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn the present paper we describe the synthesis, purification, single crystal x‐ray analysis, and nmr solution characterization, combined with restrained molecular dynamic simulations, of the cyclic hexapeptidecyclo‐(L‐Pro‐L‐Phe‐β‐Ala)2. The peptide was synthesized by classical solution methods and the cyclization of the free hexapeptide was accomplished in good yields in diluted methylene chloride solution usingN,N‐dicyclohexyl‐carbodiimide. The compound crystallizes in the monoclinic space group P21from methanol‐dichloro‐methane solution. The two identical halves of the molecule adopt in the solid state two different conformations. One β‐Ala‐L‐Pro peptide bond istrans, while the second iscis. The molecule is present in dimethylsulfoxide d6solutions as a mixture of conformational families. One of these corresponds to a C2symmetrical molecule with both β‐Ala‐Procispeptide bonds, while the second major conformation is very similar to that observed in the solid state. All Pro‐Phe segments, both in the solid state and the symmetrical and unsym‐metrical solution conformations, display ϕ,ψ angles close to that of positioni+ 1 andi+ 2 of type II β‐turns. In addition, the segments preceeded by atransβ‐Ala‐Pro peptide bond are characterized by a typicali←i+ 3 hydrogen bond, which is absent in the conformer containing acisβ‐Ala‐Pro peptide bond. The latter conformation corresponds to a new structural domain we define as

ISSN:0006-3525    

DOI:10.1002/bip.360341109

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

年代:1994

数据来源: WILEY

摘要:

AbstractAgarose films were prepared using a variety of casting conditions, heat treatments, and solvation treatments. Films represented the high temperature sol, the room temperature gel, and a high temperature state with cross‐links intact. The vacuum uv CD of the film samples varies considerably, but the similarities between the film CD and the previously reported solution CD show that dehydration per se does not affect the CD. Combining the CD results for the dried sol with the x‐ray results of Foord and Atkins leads to a description of the high temperature sol in terms of locally extended chain conformations. The CD of the gel and its peculiarly high uv absorption are satisfactorily, albeit not uniquely, interpreted in terms of the double‐helix model of the gel, in agreement with previous conformational studies based on chiroptical properties. © 1994 John Wiley&Son

ISSN:0006-3525    

DOI:10.1002/bip.360341110

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

年代:1994

数据来源: WILEY

摘要:

AbstractBombolitins are five naturally occurring heptadecapeptides acting at the membrane level and able to increase the activity of phospholipase A2. As for other peptides with similar function, the biological activity of bombolitins seems to be mainly due to their ability to form amphipathic helical structures. We synthesized and tested the retro sequence of bom‐bolitin I (retro‐bombolitin I). This peptide showed an activity similar to that of the natural sequence and was able to adopt a helical structure in the presence of an amphipathic environment consisting of SDS micelles. The secondary structure of this peptide was fully characterized by CD and nmr spectroscopy. © 1994 John Wiley&Sons,

ISSN:0006-3525    

DOI:10.1002/bip.360341111

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

年代:1994

数据来源: WILEY