Conformational Analysis Corresponding to Intra-Chain Disulfide Bridged Peptides in Proteins of Known Three-Dimensional Structure

We have carried out a systematic analysis in order to evaluate whether Intra-Chain Disulfide Bridged Peptides (ICDBPs) observed in proteins of known three-dimensional structure adopt structurally similar conformations as they may correspond to structural/functional motifs. 406 representative ICDBPs comprising between 3 to 17 amino acid residues could be classified according to peptide sequence length and main-chain secondary structure conformation into 146 classes. ICDBPs comprising 6 amino acid residues are maximally represented in the Protein Data Bank. They also represent the maximum number of main-chain secondary structure conformational classes. Individual ICDBPs in each class represent different protein superfamilies and correspond to different amino acid sequences. We identified 145 ICDBP pairs that had ≤ 0.5 Å root mean square deviation value corresponding to their equivalent peptide backbone atoms. We believe these ICDBPs represent structural motifs and possible candidates in order to further explore their structure/function role in the corresponding proteins. The common conformational classes observed for ICDBPs defined according to the main-chain secondary structure conformations; H (helix), B (residue in a isolated beta bridge), C (coil), E (extended beta strand), G (310 helix), I (pi helix), S (bend), T (hydrogen-bonded turn) were; “CHHH”, “CTTC”, “CSSS” and “CSSC” (for ICDBP length 4), “CSSCC” (length 5), “EETTEE”, “CCSSCC”, “CCSSSC” (length 6), “EETTTEE” (length 7), “EETTTTEE” (length 8), “EEEETTEEEE” (length 10), “EEEETTTEEEE” (length 11) and “EEEETTTTEEEE” (length 12).