Conformations of disulfide bridges in proteins

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Abstract
The conformational characteristics of disulfide bridges in proteins have been analyzed using a dataset of 22 protein structures, available at a resolution of .ltoreq. 2.0 .ANG., containing a total of 72 disulife crosslinks. The parameters used in the analysis include (.vphi., .phi.) values at Cys residues, bridge dihedral angles .chi.ss, .chi.i1, .chi.j1, .chi.i2, and .chi.j2, the distances Ci.alpha.-Cj.alpha. and Ci.beta.-Cj.beta. between the C.alpha. and C.beta. atoms of Cys(i) and Cys(j). Eight families of bridge conformations with three or more occurrences have been identified on the basis of these stereochemical parameters. The most populated family corresponds to the "left handed spiral" identified earlier by Richardson ((1981) Adv. Protein Chem. 34, 167-330). Disulfide bridging across antiparallel extended strands is observed in .alpha.-lytic protease, crambin, and .beta.-trypsin and this structure is shown to be very similar to those obtained in small cystine peptides. Solvent accessible surface area calculations show that the overwhelming majority of disulfide bridges are inaccessible to solvent.