Model peptides

Kinetic Aspects of Triple-Helix Formation of Peptide Models Compared with... 

The detection of the collagen-like threefold symmetric polypeptides, polyglycine4 and polyproline5, was the first help to elucidate the collagen structure using a synthetic peptide model. 

The maximum at 223 nm is remarkably high, though the chain is relatively short. Also remarkable is the higher folding velocity in comparison to the use of single-chain collagen-peptide models as shown in Fig. 22. The folding is also completely reversible. 

Bolton, J. L. Turnipseed, S. B. Thompson, J. A. Influence of quinone methide reactivity on the alkylation of thiol and amino groups in proteins studies utilizing amino acid and peptide models. Chem.-Biol. Interact. 1997, 107, 185-200. 

Endredi, G., C.-M. Liegener, M. A. McAllister, A. Perczel, J. Ladik, and I. G. Csizmadia. 1994. Peptide Models 8. The Use of a Modified Romberg Formalism for the Extrapolation of Molecular Properties from Oligomers to Polymers. Polyalanine Diamide in Its Extended Like or (f3, or (C5)n Conformation. J. Mol. Struct. (Theochem) 306, 1-7. 

McAllister, M. A., Perczel, P. Csaszar, W. Viviani, J.-L. Rivail, and I. G. Csizmadia. 1993b. Peptide Models 4. Topological Features of Molecular Mechanics and Ab Initio 2D-Ramachandran Maps. Conformational Data for For-Gly-NH2, For-L-Ala-NH2, Ac-l-Ala-NHMe and For-L-Val-NH2. J. Mol. Struct. (Theochem) 288, 161-179. Mehrotra, P. K., M. Mezei, and D. L. Beveridge. 1984. Monte Carlo Determination of the Internal Energies of Hydration for the Ala Dipeptide in the C7, C5, aR, and Pn Conformations. Int. J. Quantum Chem. Quantum Biol. Symp. 11, 301-308. 

Perczel, A., J. G. Angyan, M. Kajtar, W. Viviani, J.-L. Rivail, J.-F. Marcoccia, and I. G. Csizmadia. 1991a. Peptide Models. 1. Topology of Selected Peptide Conformational... 

Perczel, A., O. Farkas, and I. G. Csizmadia. 1996. Peptide Models XVI. The Identification of Selected HCO-l-SER-NH2 Conformers via a Systematic Grid Search Using Ab Initio Potential Energy Surfaces. J. Comput. Chem. 17, 821-834. 

Baum, J., and Brodsky, B. (1999). Folding of peptide models of collagen and misfolding in disease. Curr. Opin. Struct. Biol. 9, 122-128. 

Nakagawa, ET Kaiser. Synthesis of protected peptide segments and their assembly on a polymer-bound oxime application to the synthesis of a peptide model for plasma apolipoprotein A-I. J Org Chem 48, 678, 1983. 

Thus, the efficiency of energy transfer between donors and acceptors randomly distributed in a plane depends on R0, a, and a, and the transfer efficiency is independent of a. The important point was made that surface density of the acceptor could be 1 per 500 phospholipids for R0 > 30 A. Using these equations for different donor and acceptor concentrations, the data were matched against the different theoretical curves to obtain the R0. An example of the application of the method of Fung and Stryer(81) is the study of energy transfer between the tryptophan of a membrane protein (or peptide models of proteins) and DPH,(83) in which it was shown that efficient energy transfer can occur without any special interaction being required between DPH and the proteins in specific areas of the membrane. 

In one case, a small peptide with enzyme-like capability has been claimed. On the basis of model building and conformation studies, the peptide Glu-Phe-Ala-Ala-Glu-Glu-Phe-Ala-Ser-Phe was synthesized in the hope that the carboxyl groups in the center of the model would act like the carboxyl groups in lysozyme 17). The kinetic data in this article come from assays of cell wall lysis of M. lysodeikticus, chitin hydrolysis, and dextran hydrolysis. All of these assays are turbidimetric. Although details of the assay procedures were not given, the final equilibrium positions are apparently different for the reaction catalyzed by lysozyme and the reaction catalyzed by the decapeptide. Similar peptide models for proteases were made on the basis of empirical rules for predicting polypeptide conformations. These materials had no amidase activity and esterase activity only slightly better than that of histidine 59, 60). 

The use of disulfide linked di-a-helical peptides for the self-assembly of a heme-peptide model compounds has also been explored by Benson et al. (109). Conceptually analogous to the larger heme-protein systems utilized by Dutton and co-workers, to be detailed later, the incorporation of C4 S5mimetric Co(III)-porphyrins, based on coproporphyrin and octaethylporphyrin, resulted in helical induction comparable to that observed in the covalent PSM systems. 

Rubredoxin is an electron-transfer protein with an Fe(IlI)/Fe(lI) redox couple at -0.31 V (SCE) in water (20). Our peptide model, [Fe( Cys-Pro-Leu-Cys-OMe)2] (Z = benzyloxycarbonyl) (21) exhibits its Fe(lll)/Fe(ll) redox couple at -0.50 V (SCE) in Mc2SO (9). This is similar to the value observed for the native protein when the difference of the solvent is taken into account. When the model complex is solubilized in water by formation of micelles with addition of the non-ionic detergent, Triton X-KX), we also observed a quasi-reversible redox couple at -0.37 V (SCE) (5). The Fe(lll) complexes of Cys-X-Y-Cys peptides also exhibit a characteristic MCD band at 350 nm due to ligand-to-metal charge transfer which has also been found in oxidized rubredoxin (4). 

Table I. Redox Potentials of the [2Fe-2S]Peptide Model Conqtlexes...

Figure 4. Proposed structure of 20-peptide model complex.

Table n. Redox potentials (3-/2-) for [4Fe-4S] peptide model complexes in dichloromethane at room temperature... 

The best peptide model complex involving all the amino acid residues within 5 A of the cluster was prepared using a heptapeptide, Z-Cys-Ile-Ala-Cys-Gly-Ala-Cys-OMe, and a tripeptide, Z-Cys-Pro-Val-OMe. The redox potential of this complex in CH2CI2 was -0.83 V (SCE) which is very close to that of the native protein when the difference of solvent is consido ed (cf. Table II). A similar heptapeptide complex with a S-r-Bu ligand was found to give three CV peaks, which indicates the presence of isomers. 

Table HI. Redox Potentials of Peptide Model Complexes and Bulky Thiolate Complexes for 2-/1- and 3-/2- in DMF...

Fe-2S], synthetic, 33 64 [2Fe-2S] plant-type FCjSj core, 33 52-53 peptide model complexes, 33 51-54 redox couples, 33 53-54 reduction potentials, 33 53 [3Fe-xS], 33 54-55... 

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