Cloning and characterization of the Dictyostelium discoideum cycloartenol synthase cDNA

Cycloartenol synthase converts oxidosqualene to cycloartenol, the first car bocyclic intermediate en route to sterols in plants and many protists. Pres ented here is the first cy cloartenol synthase gene identified from a proti st, the cellular slime mold Dictyostelium discoideum. The cDNA encodes an 8 1-kDa predicted protein 50-52% identical to known higher plant cycloartenol synthases and 40-49% identical to known lanosterol synthases from fungi an d mammals. The encoded protein expressed in transgenic Saccharomyces cerevi siae converted synthetic oxidosqualene to cycloartenol in vitro. This produ ct was characterized by H-1 and C-13 nuclear magnetic resonance and gas chr omatography-mass spectrometry. The predicted protein sequence diverges suff iciently from the known cycloartenol synthase sequences to dramatically red uce the number of residues that are candidates for the catalytic difference between cycloartenol and lanosterol formation.