Stabilization of an ?-helical conformation in an isolated hexapeptide inhibitor of calmodulin

The conformational properties of two hexapeptides, Ac-LWRILW-NH(2) and its D-amino acid counterpart Ac-lwrilw-NH(2), identified as calmodulin inhibitors using mixture-based synthetic combinatorial library approaches, have been characterised by NMR and CD spectroscopy. The peptides fold into an alpha-helical conformation in aqueous solution. The observed short- and medium-range nuclear Overhauser effects were consistent with the formation of an alpha-helical structure and a reasonably well-defined set of structures was obtained by using restraints from the NMR data in simulated annealing calculations. Analysis of glycine-substitution analogues demonstrated that all the amino acids that make up the peptide sequence are important for the stabilization of the alpha-helical conformation. The results suggest that a well-defined set of interactions is indispensable to allow alpha-helix formation in this short hexapeptide.