Conformational determinants of the activity of antiproliferative factor glycopeptide.

The antiproliferative factor (APF) involved in interstitial cystitis is a glycosylated nonapeptide (TVPAAVVVA) containing a sialylated core 1 α-O-disaccharide linked to the N-terminal threonine. The chemical structure of APF was deduced using spectroscopic techniques and confirmed using total synthesis. The synthetic APF provided a platform to study amino acid modifications and their effect on APF activity, based on which a structure-activity relationship (SAR) for APF activity was previously proposed. However, this SAR model could not explain the change in activity associated with minor alterations in the peptide sequence. Presented is computational analysis of 14 APF derivatives to identify structural trends from which a more detailed SAR is obtained. The APF activity is found to be dictated by the close interplay between carbohydrate-peptide and peptide-peptide interactions. The former involves hydrogen bond and hydrophobic interactions, and the latter is dominated by hydrophobic interactions. The highly flexible hydrophobic peptide adopts collapsed conformations separated by low energy barriers. APF activity correlates with hydrophobic clustering associated with amino acids 4A, 6V, and 8V. Peptide conformations are highly sensitive to single point mutations, which explain the experimental trends. The presented SAR will act as a guide for lead optimization of more potent APF analogues of potential therapeutic utility.