Abstract
Microcystins (MC) are hepatotoxic, non-ribosomal peptides produced by several genera of freshwater cyanobacteria. In microcystin biosynthesis, racemase activities for incorporating D-glutamate and D-MeAsp/D-aspartate into the peptide backbone are required. In this study, phylogenetic analysis using microcystin biosynthesis gene-mcyF from several species of Microcystis was carried out. Thirteen MC producing strains were confirmed to possess mcyF homologue that indicates McyF would be an enzyme involved in MC biosynthesis. Sequence analysis of McyF from nine Microsystis strains were carried out. Conserved amino acid sequence motifs suggested that the McyF protein functions as an aspartate racemase rather than a glutamate racemase. Phylogenetic analysis of the D-amino acid racemase indicated that the McyF group is tightly clustered with aspartate group. Our results suggested that McyF may responsible for racemization of L-aspartate rather than racemization of L-glutamate.
