S. Kojima et al., FIBRIL FORMATION BY AN AMPHIPATHIC ALPHA-HELIX-FORMING POLYPEPTIDE PRODUCED BY GENE ENGINEERING, Proceedings of the Japan Academy. Series B Physical and biological sciences, 73(1), 1997, pp. 7-11
The alpha(3)-peptide, which comprises three repeats of the seven-resid
ue sequence Leu-Glu-Thr-Leu-Ala-Lys-Ala, was designed to form an amphi
pathic alpha-helix with a hydrophobic surface by Leu residues and a hy
drophilic surface by Glu and Lys residues, thus yielding a coiled coil
or a helical bundle structure through their association. The alpha(3)
-peptide was produced by gene engineering using Escherichia coli. Asso
ciation to a tetramer had been demonstrated by sedimentation equilibri
um analysis in a previous study. In addition to tetramerization, elect
ron microscopic observation revealed that the alpha(3)-peptide formed
''fibrils'' 5 to 10 nm in width in 10 mM potassium phosphate/0.1 M KCl
(pH 6.0). By increasing the salt concentration, the alpha(3)-peptide
formed much larger ''fibers'' assembled from many ''filaments'' runnin
g along the long axis, each of which was thinner and longer than those
observed at lower salt concentration. Hydrophobic interaction is cons
idered to be a main force responsible for forming the fibrous structur
e. However, the electrostatic features of the alpha(3)-peptide seem to
affect fibril assembly, since the shape and size of the fibrous struc
ture were altered by the ionic strength of the solution. To our knowle
dge, this is the first report to describe formation of a fibrous struc
ture by a de novo designed alpha-helix-forming peptide, and thus the a
lpha(3)-peptide with its simple sequence is considered to be a potenti
al model peptide for investigating the molecular mechanisms of fibril
formation by peptides or proteins.