Role of Cationic Residues in Fine Tuning the Flexibility of Charged Single α-helices

Abstract

A few highly charged natural peptide sequences have recently been suggested to form stable α-helical structures in aqueous solution. Here we show that these sequences represent a more widespread structural motif called 'charged single α-helix' (CSAH). We have developed two conceptually different computational methods capable of scanning large databases: SCAN4CSAH is based on sequence features characteristic for salt bridge stabilized single α-helices, while FT_CHARGE applies Fourier transformation to charges along sequences. Using the consensus of the two approaches, a remarkable number of proteins were found to contain putative CSAH domains. Recombinant fragments of 50-60 residues in length corresponding to selected hits (from myosin 6, Golgi complex associated protein-60, and mitogen-activated protein kinase M4K4) were found to adopt a highly stable α-helical structure in water. Molecular dynamic simulations of five CSAH peptides (the above three plus peptides from caldesmon and myosin 10) showed that the formation of dynamic ion-pair clusters significantly contribute to the stability of the helices. Furthermore, cationic residues were found to play a differential role in tuning the local flexibility of the CSAH domains. We conclude that sequence specific tuning of flexibility of CSAH peptides could have important role in the mechanical performance of CSAH-containing myosin motors, such as myosin 6 and 10, or in other protein functions.This work was supported by the Hungarian National Science Fund (OTKA).