Conversion of a porin-like peptide channel into a gramicidin-like channel by glycine to D-alanine substitutions

¹ IU School of Medicine
² Indiana University, School of Medicine

^* To whom correspondence should be addressed. E-mail: lguo{at}iupui.edu.

Submitted on August 16, 2005
Revised on October 4, 2005
Accepted on 19 October 2005

	Abstract

The -barrel and -helix formation as in porins and gramicidin respectively represent two distinct mechanisms for ion channel formation by -sheet proteins in membranes. The design of -barrel proteins is difficult due to incomplete understanding of the basic principles of folding. The design of gramicidin-like -helix relies on an alternating pattern of L and D-amino acid sequence. Recently we noticed that a short -sheet peptide (xSxG)6, can form porin-like channels via self-association in membranes. Here, we proposed that glycine to D-alanine substitutions of the N-formyl-(xSxG)6 would transform the porin-like channel into a gramicidin-like 12-helical channel. The requirement of an N-formyl group for channel activity, impermeability to cations with a diameter > 4 Å, high monovalent cation selectivity and the absence of either voltage gating or sub-conductance states upon D-alanine substitution support the idea of a gramicidin-like channel. Moreover, the CD spectrum in membranes is different indicating a change in regular -sheet backbone structure. The conversion of a complex porin-like channel into a gramicidin-like channel provides a link between two different mechanisms of -sheet channel formation in membranes and emphasizes the importance of glycine and D-amino acid residues in protein folding and function and in the engineering of ion channels.

Key Words: -barrel, -helix, conformation, ion-channels, lipid bilayer, peptide design