Cysteine residues in peptides

A novel method for linking sugar and cysteine residues in peptides and proteins utilizes the alkylating agent (11) to give derivatives such as (12). ... 

Dayon, L. Roussel, C. Prudent, M. Don, N. Girault, H. H. On-line counting of cysteine residues in peptides during electrosjnay ionization by electrogenerated tags and their application to protein identification. Electrophoresis 2005, 26, 238-247. 

ZiouDROU, C., M. WiLCHEK, and A. Patchornik Conversion of the L-Serine Residue to an L-Cysteine Residue in Peptides. Biochemistry 1965, 1811. 

Szaho, S., Szokan, Gy., Khlafulla, A.M., Almas, M., Kiss, C., RiU, A., and Schon, I., Configuration and racemization determination of cysteine residues in peptides hy chiral derivatization and HPLC Application to oxytocin peptides, J. Peptide Sci., 7, 316, 2001. 

Disulfide bridge (Section 27 7) An S—S bond between the sulfur atoms of two cysteine residues in a peptide or pro tein... 

A disulfide bond between cysteine residues in different peptide chains links the otherwise separate chains together, while a disulfide bond between cysteine residues in the same chain forms a loop. Such is the case, for instance, with vasopressin, an antidiuretic hormone found in the pituitary gland. Note that the C-terminal end of vasopressin occurs as the primary amide, -CONHz, rather than as the free acid. 

The catalytic mechanism in this class is based upon similar chemical principles as the mechanism of the serine proteinases. A cysteine residue in the active site is activated by a histidine imidazolium side chain and carries out a nucleophilic attack on the carbonyl carbon of the scissile peptide bond with the complex going through an acyl intermediate transition state (28,29). Certain members of this class of enzymes have pH optima in the acidic range and... 

When peptides containing four cysteine residues in the molecule are randomly oxidized, three different disulfide isomers can be formed (Scheme 1), isomer 1 with the disulfides aligned in parallel manner, isomer 2 with crossed disulfides and isomer 3 with sequential disulfides these isomers are also named in a more descriptive manner as the ribbon, globule and string-of-beads isomers. 28 The preferred formation of one of the isomers strongly depends upon the sequential topology of the cysteine residues, but also upon the sequence composition that may favor more or less globular structures with hydrophobic cores. 

Several models have been proposed for the active center of iron and sulphur in Clostridial ferredoxin in which the cysteine residues in the peptide chain participate in the sulphur bridging. Fig 9 166). Unfortunately X-ray analysis of crystals of these proteins has not been completed. It is difficult to confirm that all the irons are clustered in a single linear array 167, 168). X-ray studies of another non-heme iron protein, the high potential iron protein, hipip, from chromatium, carried out by J. Kraut (personal communication), indicate that the four irons of this molecule may be clustered in a tetrahedral array. 

ESR studies on fumarate reductase in situ have suggested1436 the presence of two [2Fe-2S] clusters and a HiPIP cluster. Examination of the occurrence of cysteine residues in the two peptides and a comparison with succinate dehydrogenase suggests that the two-iron centres are in the smaller iron-sulfur protein, while the [4Fe-4S] centre may be in either subunit. 

At neutral and slightly alkaline pH, N-chlorosuccinimide (NCS) and N-chloro-p-toluenesulfonamide (chloramine-T) oxidize methionine residues in peptides and proteins to methionine sulfoxides (31). Chlor-amine-T is more selective than NCS it does not react with tryptophan whereas NCS does. However both of these reagents react with cysteine. Treating the Ca2+-dependent protein modulator with NCS in the presence of Ca2+ resulted in selective oxidation of methionines 71, 72, 76, and possibly 109 in the modulator sequence with concomitant loss in interaction with cyclic nucleotide phosphodiesterase (32). Methionine residues have been implicated in the activation of cyclic nucleotide phosphodiesterase by the Ca2+-dependent protein modulator. 

The structure of cytochrome c determined by Dickerson and his colleagues (23, 24, 25, 26) is depicted in Figure 1. The heme group, which lies in a crevice of the essentially globular protein, is covalently bonded to the protein by thioether bridges between the porphyrin ring and two cysteine residues in the peptide chain. The iron atom is situated... 

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