Evaluation of the role of disulfide bridges plays an important part in understanding the concept of protein folding. We are investigating how slight changes - the presence vs. the absence of the cyclic amino acid proline in a certain position of the peptide-chain - in the sequence of small peptides influence their folding properties. The present studies focus on the folding of a group of small peptides found in Conus snails, α-conotoxins SI, SIA (found in Conus Striatus), and GI (Conus Geographus), under two different oxidizing conditions. Each peptide has two disulfide bridges leading to three possible regioisomers, only one of which is found in nature. Our results indicate that peptides containing the cyclic amino acid proline had very high selectivity for the natural isomer, suggesting that this amino acid enforces a structural rigidity on the peptides. This research has been supported by funding through NIH R15 GM074654-01A2 and NSF DUE 0525440.
