J. Biol. Chem., Vol. 261, Issue 22, 10017-10020, Aug, 1986
Structural analysis and amphiphilic properties of a chemically synthesized mitochondrial signal peptide
RM Epand, SW Hui, C Argan, LL Gillespie and GC Shore
Anionic phospholipids induce a marked conformational change in a synthetic
peptide corresponding to residues 1-27 of pre-ornithine
carbamyltransferase. The peptide designated, pO-(1-27)-peptide amide,
becomes more alpha-helical in the presence of cardiolipin or
dimyristoylphosphatidylglycerol but not in the presence of
dimyristoylphosphatidylcholine. The greater helix-promoting action of
anionic versus zwitterionic lipids is predicted by helix-coil transition
theory. This statistical mechanical theory also predicts that a shorter
peptide, N-acetyl-pO-(16-27)-peptide amide, has less helix-forming
tendency, even in the presence of sodium dodecyl sulfate, despite the fact
that it has a comparable number of positive charges. The
N-acetyl-pO-(16-27)-peptide amide has no helical structure in buffer with
or without dimyristoylphosphatidylglycerol but it has a small (5%) helical
content in methanol. Thus, the ability of anionic lipids to promote helix
formation requires more than the presence of cationic groups on the
peptide. The angular dependence of the hydrophobic moment of the putative
helical segment of pO-(1-27)-peptide amide demonstrates that any helical
structure which is formed would have some amphiphilic character. The
pO-(1-27)-peptide amide disrupts large lipid aggregates to form discoid
micelles about 30 to 50 nm in diameter. The ability to lyse membranes into
disc-shaped micelles is characteristic of peptides containing an
amphiphathic helix. In the case of the mitochondrial signal peptide, this
membrane-lytic behavior may contribute to the translocation of the protein
into the organelle.