ISSN:0006-3525    

DOI:10.1002/bip.360240103

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

年代:1985

数据来源: WILEY

摘要:

AbstractAn evaluation is made of the use of adenylate analogs as spatial, dimensional, and fluorescent probes of enzyme‐coenzyme binding site

ISSN:0006-3525    

DOI:10.1002/bip.360240104

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe photoexcitation of rhodopsin triggers a cascade that results in the hydrolysis of a large number of molecules of cyclic GMP. The molecular mechanism of this amplification cascade has been delineated. Transducin, a multisubunit perpheral membrane protein, is the information‐carrying intermediate in the activation of the cyclic GMP phosphodiesterase. Photoexcited rhodopsin (R*) castalyzes the exchange of GRP for GDP bound to the α‐subunit of transducin (T). About 500 molecules of Tα‐GTP are formed per absorbed photon at low light levels. Tα‐GTP, rekeased from the β‐ and γ‐subunits of transducin, then activates the phosphodiesterase by relieving an inhibitory constraint imposed by its small sununit. Each actived phosphodiesterase molecule hydrolyzes more than 100 cyclic GMP/s, giving an overall gain of more than 500,000. Photoexcited rhodopsin triggers the activation of a molecule of transducin in a millisecond, which is sufficiently rapid to enable this cascade to participate in visual excitation. Hydrolysis of GTP bound to Tαseves to restore the system to the dark state. Transducin, like the G proteins of the adenylate cyclase casecade, can be specifically ADP‐ribosylated by cholera toxin and pertussis toxin. In both cascades, labling by pertussis toxin blocks the capacity of transducin to interact with the excited receptor, whereas labeling by cholera toxin inhibits the hydrolysis of bound GTP, leading to persistent activation. Moreover, the moleculaar design of the hormone‐triggered cyclic AMP cascade is similar to that of the light‐triggered cyclic GMP cascade. It seems likely that transducin, the stimulatory G protein, the inhibitor G protein, and therasprotein are members of the same family of signal amplifiers. The study of the cyclic nucleotide cascade of vision is providing rewarding views of recurring motifs of signal

ISSN:0006-3525    

DOI:10.1002/bip.360240105

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

年代:1985

数据来源: WILEY

摘要:

AbstractA molecular model for the complex formed between the jack bean lectin concanavalin A (Con A) and glycopeptides of the complex biantennary class is described. The model was derived using coordinates for Con A determined by x‐ray crystalographic refinement techniques, with 1.75‐Å resolution data, and coordinates for the glycopeptides obtained from1H‐nmr measurements, using the nuclear Overhauser effect. Previous solution and crystallographic studies provided several constraints on the possible mode of interaction of the lectin and the glycopeptide. Examination of the model suggests that the glycopeptide binding site is defined by four loops on the protein surface made up by amino acid residues: 12–18, 98–102, 205–208, and 226–229. Within these loops, it favorable interactions with high‐affinity ligands and tose responsible for the unfavourable interactions w

ISSN:0006-3525    

DOI:10.1002/bip.360240106

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

年代:1985

数据来源: WILEY

摘要:

AbstractWe have measured the percentages ofcisandtransGly‐Pro and X‐Hyp peptide bonds in thermally unfolded type I collagen.13C‐nmr solution spectra show that 16% of the Gly‐Pro and 8% of the X‐Hyp bonds arecisin unfolded chick calvaria collagen. These results support the hypothesis thatcis–transisomerization is that rate‐limiting step in the propagation of the collagen triple helix. We have used multinuclear solid‐state nmr to study the molecular dynamics of the collagen backbone in tendon, demineralized bone, and intact bone as a function of temperature, hydration, and pH. These studies show that collagen backbone motions are characterized by a broad distribution of correlation times, τ, covering the range from 10−4to 10−9s. In the case of nonmineralized collagen, the root‐mean‐square fluctuations in azimuthal angle, γrms, range from ca. 10° when τ ∼ 10−9s to ca. 30° when τ<10−4s; in the case of bone collagen, γrmsvalues are about half as large as those found in nonmineralized collagen. Backbone motions are negligible at temperatures below −25°C. This is also the case at 22°C when demineralized bone collagen is lyophilized. In contrast, flexibility of hydrated demineralized bone collagen greatly increases as pH is lowered from 7 to 2. The more limited flexibility observed at neutral pH is a consequence of the intermolecular interactions that contribute to fibril organization and strength. However, the fibrils retain significant flexibility at physiological pH, enabling them to distribut

ISSN:0006-3525    

DOI:10.1002/bip.360240107

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

年代:1985

数据来源: WILEY

摘要:

AbstractPhenomena studied by fluorescence spectroscopy, including differential perturbations of dye fluorescence by variations in DNA composition and interdye energy transfer, can be applied to cytological studies of chromosome structure, replication, and repair. When combined with fluorescence‐activated flow sorting, fluorescent differentiation between metaphase chromosomes can be exploited to obtain recombinant DNA libraries enriched for all or parts of individual chromosomes. Cloned DNA segments from such libraries continue to find application in studies of human chromosome structure and function and in molecular linkage analyses, thus leading to molecular genetic investigations of human disease state

ISSN:0006-3525    

DOI:10.1002/bip.360240108

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

年代:1985

数据来源: WILEY

摘要:

AbstractA multistep computational scheme was used to deduce possible conformations for a cyclic antagonist analog of somatostatin that has been reported by Coy and coworkers. An algebraic algorithm was used to find dihedral angles that give cyclic structures, the energy was computed for these structures, the lower‐energy structures were classified into conformational families, the energy was minimized for the lowest‐energy member of each family, and finally, the structures from energy minimization were reclassified. Analysis revealed seven distinct conformational families that contain reverse turns. The families differ in the position of the turns in the primary sequence; frame‐shifted turns are observed at each possible pos

ISSN:0006-3525    

DOI:10.1002/bip.360240109

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

年代:1985

数据来源: WILEY

摘要:

AbstractPeptide hormones and neurotransmitters are functional amphiphilic substances that deploy their chared and nonpolar substituents as required for traversing aqueous phases en rout to their ultimate transfer into the lipid‐rich environment of their membrane‐embedded receptors. As a means of determining the role(s)that cellular membrane lipids may play in mediating these events, we describe an experimental approach, using high‐resolution1H‐and13C‐nmr spectroscopy, for delineation of the structures of complexes between the (neurotransmitter pentapeptide) enkephalins and micellar and vesicular phospholipid particles. Residue‐specific enkephalin interactions with lipid are identified; affinity constants for the hydrophobic component(s) of peptide/lipid association are calculated for enkephalin and several of its analogs; and comparisons with morphine are presented. Finally, based on molecular details obtained from nmr experiments, a model is proposed for the encoutner of a peptide hormone with a phospholipid membr

ISSN:0006-3525    

DOI:10.1002/bip.360240110

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

年代:1985

数据来源: WILEY

摘要:

AbstractTwo studies are diescribed in which synthetic peptides have been designed and examined to address biochemical problems inherent in hydorphobic environments: (1) The cyclic hexapeptide cyclo‐(D‐Tyr(Bzl)‐Gly‐Ile‐Leu‐Gln‐Pro) was synthesized as a model of an interior β‐turn from the protein lysozyme. Conformational analysis by proton nmr methods, including two‐dimensional nulcear Overhauser effect spectroscopy, revealed that the model peptide adopts one conformation in chloroform/dimethyl sulfoxide (98.2) and tetramethylene sulfone solutions. The conformation consists of two linked β‐turns, one with the same sequence (Gly‐Ile‐Leu‐Gln) and geometry (Type I) as the protein turn. (2) Major portions of the λ‐receptor protein (LamB) signal sequences fromE. coliwildtype and mutant strains have been synthesized. The conformational properties and membrane interactions of these synthetic signal peptides correlate with thein vivoexport function of the wild type and mutant strains. Functional signal sequences are significantly richer in α‐helix in aaqueous trifluoroethanol, lysolecithin, or sodium do‐decyl sulfate solution than is a n

ISSN:0006-3525    

DOI:10.1002/bip.360240111

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

年代:1985

数据来源: WILEY

摘要:

AbstractA general approach to study peptide structure is presented using three areas of ongoing research in our laboratories. The first involves the molecular basis for taste of peptide derivatives. We synthesized dipeptides based onL‐aspartyl‐α‐aminocycloalkane carboxylic acid methyl ester. Ahomologousseries of cycloalkane derivatives was studied. The cyclopropane, cyclobutane, and cyclopentane derivatives are sweet, the cyclohexane and cycloheptane peptides are bitter, and the cyclooctane homolog is tasteless. The related acyclic analogL‐aspartyl‐aminoisobutyric acid methyl ester is sweet, while theL‐aspartyl diethyl glycine carboxylic acid methyl ester is tasteless. A model is presented to explain these experimental observations. The second area involves depsipeptides asisostericreplacements of α‐hydroxy acids for amino acid residues in peptide chains. We have synthesized sequentially defined polydepsipeptides as model systems for polypeptides. A detailed analysis of the conformational order for these polydepsipeptides is presented. The third area involves partial retro–inverso peptide modifications ofisomericcyclic enkephalin analogs, which illustrate the relationship between the modification and biological activity. We are probing the intramolecular hydrogen‐bonding features for these biologically active molecules. From such findings we are relating the structural and conformational preferences deduced from spectroscopy and molecular mechanics to

ISSN:0006-3525    

DOI:10.1002/bip.360240112

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

年代:1985

数据来源: WILEY