title: Conversion of a porin-like peptide channel into a gramicidin-like channel by glycine to D-alanine substitutions.
abstract: The beta-barrel and beta-helix formation, as in porins and gramicidin, respectively, represent two distinct mechanisms for ion channel formation by beta-sheet proteins in membranes. The design of beta-barrel proteins is difficult due to incomplete understanding of the basic principles of folding. The design of gramicidin-like beta-helix relies on an alternating pattern of L- and D-amino acid sequences. Recently we noticed that a short beta-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 beta(12)-helical channel. The requirement of an N-formyl group for channel activity, impermeability to cations with a diameter >4 A, high monovalent cation selectivity, and the absence of either voltage gating or subconductance states upon D-alanine substitution support the idea of a gramicidin-like channel. Moreover, the circular dichroism spectrum in membranes is different, indicating a change in regular beta-sheet backbone structure. The conversion of a complex porin-like channel into a gramicidin-like channel provides a link between two different mechanisms of beta-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.
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
authors.forename: Jyothi
authors.initials: J
authors.lastname: Thundimadathil
authors.forename: Roger W
authors.initials: RW
authors.lastname: Roeske
authors.forename: Lili
authors.initials: L
authors.lastname: Guo
mesh_terms: D000409:Alanine / Q000737:chemistry*; D000596:Amino Acids / Q000737:chemistry; D002412:Cations; D002462:Cell Membrane / Q000378:metabolism; D002942:Circular Dichroism; D004573:Electrolytes; D005998:Glycine / Q000737:chemistry*; D006096:Gramicidin / Q000737:chemistry*; D007473:Ion Channels / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry; D018272:Porins / Q000737:chemistry*; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared; D013997:Time Factors; D014364:Tryptophan / Q000737:chemistry
chemical_list: D000596:Amino Acids; D002412:Cations; D004573:Electrolytes; D007473:Ion Channels; D008051:Lipid Bilayers; D010455:Peptides; D018272:Porins; D006096:Gramicidin; D014364:Tryptophan; D000409:Alanine; D005998:Glycine