摘要:

Analogs of theSaccharomyces cerevisiaeα‐mating factor, Trp‐His‐Trp‐Leu‐Gln‐Leu‐Lys‐Pro‐Gly‐Gln‐Pro‐Met‐Tyr, where Lys7and Gln10were replaced with Cys, Cys(CH3), or Ser, were synthesized using solid‐phase procedures on a phenylacetamidomethyl resin. Cyclo7,10[Cys7,X9,Cys10,Nle12]α‐factor, where X = D‐Val, D‐Ala,l‐Ala and Gly, were prepared by on‐resin cyclization using thallic trifluoroacetate in yields of 20–30%. Linear sulfhydryl‐containing peptides were generated from their corresponding cyclic peptide by treatment with dithioerythritol in basic solution. In the linear analogs, replacement of both Lys7and Gln10with a cysteine residue resulted in an over 100‐fold loss of the biological activity when compared with the native pheromone. The corresponding cyclic disulfides were 5–10‐fold more active than their sulfhydryl‐contaihing homologs, and cyclo7,10[Cys7,L‐Ala9,Cys10,Nle12] α‐factor was 50‐fold more potent than linear analogs containing Ser or Cys(CH3) in positions 7 and 10. Binding competition studies indicated that all analogs had low affinity for the α‐factor receptor and there was a poor correlation between binding and activity in a growth arrest assay. A cyclic analog in which residues 8 and 9 were replaced by 5‐aminopentanoic acid was not biologically active. Based on NMR studies, all cyclic peptides have a higher tendency to form β‐turns spanning residues 7–10 than their less active linear counterparts. The results provide strong evidence that

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01336.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Replacement of the α‐carbon with a nitrogen in α‐amino acids gives rise to azaamino acids. Most examples of azaamino acids that have been incorporated into peptides are linear analogs, in which conformational effects are restricted to the immediate vicinity of the urea bond. In contrast to the linear azaamino acids, the heterocyclic analogs might be expected to exhibit stronger conformational preferences, but examples of this class of azaamino acids are very limited. We synthesized tetrahydrophthalazine (THPhth) as a constrained phenylalanine analog and elaborated it into the model pseudotripeptideN‐{([N‐alanyl]‐1,2,3,4‐tetrahydro‐2‐phthalazinyl)carbonyl)}‐L‐alanine (1). As shown by NMR studies, tetrahydrophthalazine 1A has a secondary structure in which ψTHPhth is fixed at 16–18° and there are two equal populations ofcisandtransamide bonds from theN‐terminal

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01337.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

S‐4‐methoxytrityl cysteine was synthesized and converted into the corresponding Fmoc‐Cys(Mmt)‐OH by its reaction with Fmoc‐OSu. As compared to the corresponding Fmoc‐Cys(Trt)‐OH, theS‐Mmt‐function was found to be considerably more acid labile. QuantitativeS‐Mmt‐removal occurs selectively in the presence of groups of thetertbutyl type andS‐Trt by treatment with 0.5–1.0% TFA. The new derivative was successfully utilized in the SPPS of Tyr1‐somatostatin on 2‐chlorotrityl resin. In this synthesis groups of the Trt‐type were exclusively used for amino acid side‐chain protection. Quantitative cleavage from the resin and complete deprotection was performed by treatment with 3% TFA in DCM–TES (95:5) for 30 min at RT. We observed no reduction of tryptophan under

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01338.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The effect of Zn(II) binding on the structure of bovine α‐lactalbumin (LA) was investigated. α‐Lactalbumin, a regulatory subunit of lactose synthase, binds Ca(II) and Zn(II) at different sites in a mutually non‐exclusive manner. The structures of the metal‐depleted form of LA (apo‐LA) and Ca(II)‐bound LA (holo‐LA) have been well characterized. Here, the effect of Zn(II) binding on the structure of holo‐LA has been investigated by comparison with the structure of holo‐LA and apo‐LA using CD and NMR spectroscopy. The CD spectrum of Zn(II)‐holo‐LA was similar to that of holo‐LA, but the intensity of the negative peak in near‐UV region was decreased. Zn(II) binding to holo‐LA produced only small changes in NMR chemical shifts, but the integral volumes of the cross‐peaks of NOESY signals in cluster II, which is in the vicinity of Zn(II) binding site, were affected. Zn(II) binding induces a local structural change on the holo‐LA, but it does not induce a large backbone confo

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01339.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Oxidation of nonapeptide dithiol (2) with K3Fe(CN)6leads to either monomeric disulfide (4) or antiparallel and parallel dimeric disulfides (3a and 3b) depending upon reaction conditions. When exposed to small amounts of thiols or cyanide in aqueous solution, these three species interconvert to an equilibrium mixture of 2:1:8 (3a: 3b: 4). © Munksgaard 1996. © Munksgaard 199

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01340.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

A theoretical method was applied to consensus sequences of several members of the snake toxin family as a further approach to examining their conformational homology. Some secondary‐structure predictions as well as hydropathy profiles were also examined. A comparison of long neurotoxins themselves reveals a high homology degree. However, theirC‐terminal fragments show poor homology and theN‐terminal fragments appear as the region of maximum variability. Moreover, when the matrix includes the consensus sequence of the genusLaticauda(LNTX1), lacking the disulfide bridge 31–35, the method detects a lower conformational homology in a molecular region centered at position 31. Unlike long neurotoxins, theN‐terminal segments of short neurotoxins show a high homology degree, but when comparing short with long neurotoxins, a poor correlation is found in this zone of the molecule. Cytotoxins studied exhibit an excellent conformational homology except when the consensus sequence of cytotoxin homologues CTXE is one of the proteins in the matrix. A comparison between cytotoxins and short neurotoxins reveals homology only in two segments belonging to a β‐sheet structure. A considerable degree of homology is found between the short neurotoxin group and calciseptin and fasciculin as well as between the long neurotoxin group and κ‐neurotoxins. ©

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01341.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

With very low concentrations of anionic detergents, such as sodium dodecyl sulfate (SDS) and Aerosol OT (AOT), it is possible to solubilize proteases in organic solvents, while retaining enzymatic activity. For example, the SDS–subtilisin BPN′ complex catalyzes transesterification of Ac‐Phe‐OMe in ethanol with akcat/Kmof 36 M−1S−1for mutant M1 and 39 M−1S−1for the wild type. By comparison, M1 suspended in ethanol is approximately 1000‐fold less active, with akcat/Kmof 0.03 M−1s−1. Similarly, AOT complexes of α‐chymotrypsin were found to be approximately 1000 times more active (kcat/Km= 100‐350 M−1s−1) than the suspe

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01342.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Trifluoroacetic acid (TFA) is a common reagent in both solid‐phase and solution peptide synthesis. It is used for the deprotection and/or cleavage of the synthesized peptide from the resin. The use of TFA under these standardized conditions is thought to be sufficiently mild, thereby preventing degradation of the desired product. However, peptides of the general structure R1‐(N‐alkyl X1)‐X2‐R2are hydrolyzed by standard TFA solid‐phase peptide synthesis (SPPS) cleavage/deprotection conditions providing fragments R1‐(N‐alkyl X1)‐OH and H‐X2‐R2. The fragmentation is observed during a TFA cleavage both from the resin and in solution. The hydrolysis is proposed to proceed via an oxazolone‐like intermediate in which equilibration of the chiral center of theN‐alkylated residue occurs. This mechanism is supported by H/D exchange as observed by MS and NMR in conjunction wit

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01343.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Peptides containing backbone thioamides (endothiopeptides) have been synthesized utilizing thioacylation under solid‐phase conditions. The thioacylations were performed by activatingN‐protected amino monothio acids with the phosphorus‐containing coupling reagent 6‐nitrobenzotriazol‐1‐yloxytris(pyrrolidino)phosphonium hexafluorophosphate (PyNOP). This method avoids the use of P4S10‐based O/S‐exchange reagents, and it is thus amendable to amino acids with side‐chain amides. Synthesis of endothio analogs of biologically active peptide such as pGlu‐ψ[CSNH]‐His‐Pro‐NH2(TRH) and Leu‐Gln‐ψ[CSNH]‐Leu‐Lys demonstrated this feature. Proton and carbon NMR spectra of the TRH analog verified the sequential position of its thioamide function. Compatibility of endothiopeptides with allyl‐protecting groups was studied, and 1,8‐diazabicyclo[5,4,0]undec‐7‐ene (DBU) was evaluated as a s

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01344.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Recombinant human erythropoietin (rHuEPO) is biologically functional when in a monomeric state; upon extensive heating, rHuEPO forms a dimer. The nature of this dimeric linkage was investigated after isolation of the dimer by gel filtration. The dimer fraction was subjected to tryptic digestion, and the peptides were separated by reversed‐phase HPLC. SDS‐PAGE,N‐terminal sequencing, capillary electrophoresis and mass spectrometry (both liquid‐chromatographic electrospray and matrix‐assisted laser desorption ionization) were employed to compare the tryptic peptides from heat‐treated rHuEPO and untreated rHuEPO. Results demonstrated that elevated heat broke the intramolecular disulfide bond between Cys‐7 and Cys‐161 and an intermolecular disulfide bond then formed from these residues, producing a covalently linked rHuEPO homodimer. Dimer formation was also mathematically modeled and shown to fit a simple equilibrium. ©

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01345.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY