Homology of the predicted secondary structures of the N-terminal fragments of preproteins.

Secondary structures of the N-terminal fragments of 18 preproteins were analysed taking advantage of the method of Chou & Fasman (Biochemistry, 1974, 13, 222-245; J. Mol. Biol., 1977, 115, 135-175) and the known sequences of amino acid residues. Positions of alpha-helices, beta-sheet structures and beta-turns in the linear primary structure of preproteins have been proposed. Also it has been suggested that the three-dimensional structures of the N-terminal fragments of preproteins are homologous, irrespective of the differences in their primary structures, length of polypeptide chains, and function. A three-dimensional model of the N-terminal fragment is given, comprising the regions responsible for transport and removal of the signal peptide from preprotein. The location of prelipoprotein region responding to signal protease, and the substrate spatial requirements of this enzyme have been hypothesized.