NMR investigations of structural and dynamics features of natively unstructured drug peptide – salmon calcitonin: implication to rational design of potent sCT analogs


Dinesh Kumar, Centre of Biomedical Magnetic Resonance, Sanjay Gandhi Post-Graduate Institute of Medical Sciences Campus, Raibareli Road, Lucknow-226014, Uttar Pradesh, India. E-mail: 14feb.dinesh@gmail.com


Backbone dynamics and conformational properties of drug peptide salmon calcitonin have been studied in aqueous solution using nuclear magnetic resonance (NMR). Although salmon calcitonin (sCT) is largely unfolded in solution (as has been reported in several circular dichroism studies), the secondary Hα chemical shifts and three bond HN–Hα coupling constants indicated that most of the residues of the peptide are populating the α-helical region of the Ramachandran (ϕ, ψ) map. Further, the peptide in solution has been found to exhibit multiple conformational states exchanging slowly on the NMR timescale (102–103 s−1), inferred by the multiple chemical shift assignments in the region Leu4–Leu12 and around Pro23 (for residues Gln20–Tyr22 and Arg24). Possibly, these slowly exchanging multiple conformational states might inhibit symmetric self-association of the peptide and, in part, may account for its reduced aggregation propensity compared with human calcitonin (which lacks this property). The 15N NMR-relaxation data revealed (i) the presence of slow (microsecond-to-millisecond) timescale dynamics in the N-terminal region (Cys1–Ser5) and core residues His17 and Asn26 and (ii) the presence of high frequency (nanosecond-to-picosecond) motions in the C-terminal arm. Put together, the various results suggested that (i) the flexible C-terminal of sCT (from Thr25–Thr31) is involved in identification of specific target receptors, (ii) whereas the N-terminal of sCT (from Cys1–Gln20) in solution – exhibiting significant amount of conformational plasticity and strong bias towards biologically active α-helical structure – facilitates favorable conformational adaptations while interacting with the intermembrane domains of these target receptors. Thus, we believe that the structural and dynamics features of sCT presented here will be useful guiding attributes for the rational design of biologically active sCT analogs. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.