摘要:

Acacetin (5,7‐dihydroxy‐4‐methoxy flavone) is a flavone intrinsically present in the seeds ofCarthamus tinctorius.Carmin is a multimeric, high molecular weight protein from the seeds ofCarthamus tinctorius.The association constant of interaction of acacetin and carmin is maximum at 37.2 °C with a value of (3.96±0.61)× 104M−1as measured by fluorescence quenching. Acacetin has at least two binding sites on carmin. The interaction follows pseudo‐first‐order kinetics with a reaction rate constant of 3.4 ± 0.4 s−1. The titration calorimetric data suggest that binding sites for acacetin and its structural analogue, biochanin A, are conserved. The interaction does not affect the association‐dissociation equilibrium of the protein. Also, the binding does not induce any significant conformational changes in the protein as monitored by circular dichroic spectra. Biochanin A (5,7‐dihydroxy‐4′‐methoxyisoflavone), a structural analogue, interacts with carmin with an association constant of (9.33 ± 1.44) × 104M−1at 36.9 °C. This indicates that the stereochemistry of the ligand plays an important role in the binding process of flavone to protein. Interaction studies of chemically modified lysyl and tryptophanyl groups separately, and lysyl and tryptophanyl groups sequentially, in the protein carmin with the ligands reveal the involvement of tryptophanyl residues in the binding process and show that it is predominantly an entropically driven hydrophobi

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01080.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

N‐Alkylation, and particularlyN‐farnesylation, of bioactive peptides might be of wide interest: first, to increase peptide bioavailability by decreasing their elimination and by favouring their transport through biological membranes; second, to target peptides to cellular membranes; and third, to generate therapeutic double‐substrate inhibitors of enzymes such asras‐farnesyltransferase. We report the synthesis of novelN‐farnesyl amino acids [(N‐Frn) amino acids]. We have synthesized (N‐Frn)MetOCH3, (N‐Frn)ValOBz and (N‐Frn)PheOCH3, by alkylation of the corresponding natural amino acid esters. In order to demonstrate the feasibility of the introduction of (N‐Frn) amino acids into peptides, we have synthesized representative dipeptide analogs: Cys‐(N‐Frn)ValOBz, Phe‐(N‐Frn)ValOBz, Lys‐(N‐Frn)ValOBz, Phe‐(N‐Frn)MetOCH3, Glu‐(N‐Frn)MetOCH3, Ser‐(N‐Frn)MetOCH3, Trp‐(N‐Frn)PheOCH3, and Pro‐(N‐Frn)PheOCH3, We also describe the synthesis of the model peptide Cys‐Val‐Phe‐(N‐Frn)MetOCH3, which is derived from the tetrapeptide CysValPheMet inhibi

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01081.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Nα‐Fmoc serine and its corresponding pentafluorophenyl ester were glycosylated with the1,2‐transperacetates of the disaccharides galabiose and cellobiose. Complete stereoselectivity and 52‐75% yields were obtained under boron trifluoride etherate promotion. Lower yields and loss of stereoselectivity were obtained when thioglycosides. trichloroacetimidates or glycosyl bromides were employed as glycosyl donors. The glycosylated building blocks were used in solid‐phase synthesis of derivatives of a helper T cell immunogenic peptide consisting of amino acids 52‐61 from hen‐egg lysozyme.1H‐NMR spectroscopy in DMSO‐d6showed that the peptide moiety of the glycopeptides assumed random conformations which were not influenced by glycosylation at dif

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01082.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The total enzymatic synthesis of a model peptide Leu‐enkephalin on a preparative scale was accomplished in the so‐called solvent‐free system. The syntheses were carried out in a rotary glass homogenizer by admixing solid reactants with native proteases and Na2CO3· 10H2O. The most feasible way leading to biologically active Leu‐enkephalin, was based on the strategy of 2 + (1 +2) condensation catalyzed by α‐chymotrypsin, thermolysin and papain for the final segment coupling. Subtilisin was used for the ester hydrolysis of peptide intermediates. Alternative strategies as well as the influence of several reaction conditions on the yield of the protease‐catalyzed synthesis of Leu‐enkephalin or Leu‐enkephalin amide were also investigated.

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01083.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Despite similar tripeptideN‐termini, dermorphin (Tyr‐D‐Ala‐Phe‐Gly‐Tyr‐Pro‐Ser‐NH2) and dermenkephalin (Tyr‐D‐Met‐Phe‐His‐Leu‐Met‐Asp‐NH2), naturally occuring opioid peptides from frog skin, exhibit high affinity but contrasting selectivity for the μ‐ and δ‐opioid receptors, respectively. Structure‐activity relationship studies have shown that theN‐terminal tripeptide, Tyr‐D‐Xaa‐Phe (where Xaa is either Ala or Met), is necessary for binding with both the μ‐ and δ‐receptors while the nature and/or the conformation of theC‐terminus His‐Leu‐Met‐Asp‐NH2of dermenkephalin are responsible for addressing the peptide to the δ‐receptor. In order to examine the conformational characteristics that are related to the selectivity of dermenkephalin towards the δ‐receptor, 50 NOE restraints (10 between nonadjacent residues), and 7 dihedral angles, derived from a two‐dimensional1H‐NMR study of dermenkephalin in dimethyl sulfoxide, were used in simulated annealing and energy minimization procedures. Twenty‐four resulting conformers (60% of the generated structures) with no severe distance restraint violation were pooled into seven groups and three related families. These 24 conformers show close proximity between the two methionine residues,S‐shaped structures, mean planes ofN‐terminal andC‐terminal moieties almost at right angles to each other, aC‐terminus region above the plane of theN‐terminal region andg−as preferential orientation in the side chain of the. Aside these similarities, families of conformers differ by the preferential orientation in the side chain of Tyr (torg−) and proximity between Tyr and Asp, or Tyr and theC‐terminus. In contrast to previous models, practically no β‐turn structures exist for dermenkephalin, most of the NH hydrogen bonds participating to γ‐turns. The possible relationship between the conformational char

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01084.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The solution conformation of the pheromone biosynthesis activating neuropeptide (PBAN) of the mothHelicoverpa zeahas been determined using homonuclear two‐dimensional nuclear magnetic resonance techniques and distance geometry‐restrained energy minimization. The insect peptide hormone showed a random distribution of conformers in aqueous solution, whereas in a less polar medium of trifluoroethanol and water, a reordering process was observed. In particular, theC‐terminal region (Phe‐Ser‐Pro‐Arg‐Leu‐NH2) adopts a type I′β‐turn conformation, residues 20‐27 are in a helix conformation, and residues 1‐19 exhibit a high degree of flexibility. Direct observation of theC‐terminal β‐turn configuration of PBAN is consistent with a previous report that showed a rigid, cyclic analog of theC‐terminal pentapeptide of PBAN retained pheromonotropic activity [Nachman, R.J., Kuniyoshi, H., Roberts, V.A., Holman, G.M.&Suzuki, A. (1993).Biochem. Biophys. Res. Commun.661‐666], Furthermore, our results show no interaction between theC‐terminal turn and the rest of the polypeptide chain, thus providing further evidence that theC‐terminal turn is indeed the important conformation recognized by

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01085.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

In order to investigate the biological role of the δ‐amino groups of the Orn residue in gramicidin S, the four analogs, [Ser2]‐, [Ser2,2′]‐, [Glu2]‐ and [Glu2,2′]‐gramicidin S were synthesized by a solution method. Except for the last one, these analogs show antibiotic activity to a certain extent against gram‐positive micro‐organisms, but the activities are weaker than that of gramicidin S. These results indicate that the δ‐amino group of the Orn residue is quite important for exhibiting of the activity of gramicidin S, but is not essential to the activity. NMR and CD studies of these analogs indicate that these analogs possess four intramolecular hydrogen bonds between the Val and Leu residues similar to those of GS, and the removal or diminution of the δ‐amino group of ornithine residues give the considerable influence to the dihedral angle of NαH‐CαH of D‐Phe residues and consequently affect the type II′β‐turn structure of the

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01086.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Two crystal structures of a nonapeptide (anhydrous and hydrated) containing the amino acid residue α,α‐di‐n‐butylglycyl, reveal a mixed 310‐α‐helical conformation. Residues 1‐7 adopt φ, ψ values in the helical region, with Val(8) being appreciably distorted. The Dbg residue has φ, ψ values of ‐40, ‐37° and ‐46, ‐407° in the two crystals with the two butyl side chains mostly extended in each. Peptide molecules in the crystals pack into helical columns. The crystal parameters are: C50H91N9O12, space groupP21, witha= 9.789(1)Å;,b= 20.240(2) Å.c= 15.998(3) Å.β= 103.97(1):Z= 2,R=10.3% for 1945 data observed<3σ(F) and C50H91N9O12· 3H2O, space groupP21witha= 9.747(3)Å,b= 21.002(8) Å,c= 15.885(6) Å, β= 102.22(3).Z= 2.R=13.6% for 2535 data observed<3σ(F) The observation of a helical conformation at Dbg suggests that the higher homologs in the α,α‐dialkylated glycine series also have a tendency to s

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01087.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The differences in the conformational properties of ovine (o) and human (h) CRH in aqueous solution, structure‐inducing TFE and in the presence of detergent micelles and lipid vesicles have been investigated by circular dichroism, Fourier transform infrared spectroscopy, NMR and dynamic light scattering. o‐CRH was found to exist as a monomer with little regular structure in dilute aqueous solution. Association at concentrations higher than 10−3mol/L results predominantly in dimers. The induction of a substantial amount of intermolecular β‐structure seems to be the result of interactions of theC‐terminal hexapeptide and theN‐terminal region 6‐12 of o‐CRH chains in antiparallel orientation. In contrast, h‐CRH exhibits a high tendency of association which is highly sensitive to the pH. The formation of tetramers at millimolar peptide concentration is related to a helical content of ca. 50%. The potentially helical, highly hydrophobic region 6‐20 enlarged by more hydrophobic residues in position 23 and 25 is proposed to stabilize the h‐CRH associates. In the presence of structure inducing TFE (<40%v) both CRH peptides exist as monomers. o‐CRH reveals about 72% helicity, in h‐CRH the formation of about 85% helix is observed. The differences in helicity of the two CRH molecules are located in theC‐terminal heptapeptide, as concluded on the basis of NMR studies. Both peptides bind to detergent micelles at pH 4 as well as 7.4 associated with an increase in the α‐helical content. Interaction of the two peptides with DMPC vesicles was found exclusively at pH 4. Above the phase transition temperature of DMPC the α‐helical content in h‐CRH increases slightly; however, o‐CRH reveals a substantial amount of β‐type structure. The intramolecular type of β‐structure is associated with a deeper insertion of the o‐CRH region 6‐12 into the hydrophobic region of the lipid bilayer, whereas the corresponding region of h‐CRH is kept in the bilayer surface. The higher helicity of h‐CRH might explain to some extent its higher affinity to the CRH receptor, CRH antib

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01088.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The conformational analysis and electrostatic properties of the monomeric sequence V‐G‐G‐V‐G of the glycine‐rich regions of elastin is presented with the aim of explaining NMR and CD experimental results. On the basis of the molecular model NH3−‐V‐G‐G‐V‐G‐COO−, Gaussian 92 quantum‐molecular computations were performed by using principally anab initiomethod at the 3‐21G level and AM1. The occurrence of local secondary structures and of βI, βII, βII′ and VIa turns is discussed. Our results clearly demonstrate that the transconformations βI → half turn (which was invoked to explain experimental results) and βI→βII′ a

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01089.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY