Two-dimensional NMR and structure determination of salmon calcitonin in methanol.

The structure of the 32-residue peptide salmon calcitonin (sCT) in 90% MeOH-10% H2O has been investigated by two-dimensional NMR techniques and molecular modeling. Sequential assignments for nearly all of the 32 spin systems have been obtained, and results indicate that the heptaresidue loop formed by the disulfide bond between Cys-1 and Cys-7 is followed by an alpha-helical segment from Val-8 through Tyr-22. A region of conformational heterogeneity is observed for residues 20-25, resulting from the slow isomerism of the cis and trans forms of Pro-23. The C-terminal segment is found to exist in an extended conformation.