The development of a model of Alpha helix formation for transmembrane peptides

Abstract

Researchers have studied the folding and binding properties of peptides in water for many years, but only recently has anyone attempted to explore those same tendencies in an environment similar to that of a transmembrane protein incorporated into the phospholipid bilayer of the cell. To this end, we have been working on the synthesis of a group of peptides with the general sequence +H3N-Ala2-Leu3-Ala7-Trp-Ala-X-Ala10-Lys6-COOH, where we will substitute all twenty naturally occurring amino acids into position X. We have successfully synthesized and purified the peptide in which the guest position X is filled by an isoleucine-due to the difficulty of the sequence involved, we have been unable to synthesize and purify eighteen of the remaining nineteen. Peptides, once synthesized, are characterized by MALDI mass spectrometry and HPLC and purified peptides are studied using circular dichroism (CD) spectroscopy to determine the a-helicity. Initial results suggest that the transmembrane environment will indeed alter the propensities of the various amino acid residues to form a-helices, though to what degree still remains to be seen. Once complete, this study should make it possible to determine a system for predicting a-helix formation in membrane proteins and determine the basic rules that guide such helix formation.