Electrostatic Interactions Modulate the Structure and Dynamics of Calcitonin Gene-Related Peptide

Abstract

Calcitonin gene-related peptide (CGRP) is an intrinsically disordered, 37 residue neuropeptide that acts as a potent vasodilator. It is a member of the calcitonin peptide (Ct) family, together with amylin, calcitonin and adrenomedullin. Understanding how sequence variations affect the conformation and dynamics of these genetically and functionally related IDPs is of considerable interest. While the secondary structural preferences of these peptides have been experimentally determined, the tertiary structural preferences are more challenging to detect due to fast reconfigurations of the backbone over a wide range of conformations, and to the very low solubility of certain Ct family peptides. High resolution time-resolved techniques are needed.We use a nanosecond-resolved spectroscopic technique based on tryptophan triplet quenching by cystine to detect tertiary contact formation in CGRP under varying solvent and temperature conditions. Using this technique we had previously found that conserved structural elements of amylin and CGRP induce compact states, characterized by short end-to-end distances(1,2). Here we compare contact formation rates of wild type and mutant CGRPs with different net charge. We find that electrostatic interactions modulate the degree of compaction of CGRP. The observed difference between CGRP and amylin can be rationalized in terms of electrostatic interactions. Interestingly, even with a net charge of +6, CGRP remains more compact in aqueous solvent than in denaturant with high ionic strength, indicating strong attractive intra-molecular interactions. Overall our data are consistent with a common mechanism driving compaction in CGRP and amylin, with electrostatic interactions modulating the degree of compaction in CGRP. We discuss our findings in relation to secondary structural preferences of these peptides and discuss their possible functional role.1 Vaiana S.M. et al. Biophys. J. 97 2009.2 Sara M. Sizemore et al.2012 Biophys. J, Supplement, Abstract.