[Superspiralized alpha-spiral. 1. Distribution of nonpolar residues in the hydrophobic core]

Distribution of nonpolar residues in the hydrophobic core (a and d positions) of fibrillar proteins in the form of alpha-helical coiled-coil has been studied. It was shown that concentration of large nonpolar residues (Phe, Trp) in a and d positions would not stabilize this structure; amino acids with smaller nonpolar side chains (Leu, Ala, Val, Ile, Met) are preferable, and Leu is the most preferred amino acid in the hydrophobic core; nonpolar residues with branching at the C beta atom (Val, Ile) prefer the a to the d position. The results obtained show that the distribution of nonpolar residues in the a and d positions of the alpha-helical coiled-coil cannot be only accounted for hydrophobic interactions between nonpolar residues of adjacent helices in the considered structure.