THE STREPTOMYCES-TENDAE TU901 L-LYSINE 2-AMINOTRANSFERASE CATALYZES THE INITIAL REACTION IN NIKKOMYCIN-D BIOSYNTHESIS

Protein P8 was previously identified as a putative nikkomycin biosynth esis protein. The gene (nikC) encoding protein P8 was cloned from the Streptomyces tendae Tii901 nikkomycin gene cluster and sequenced. The nikC gene was inactivated by inserting a kanamycin resistance cassette ; the mutant did not produce the biologically active nikkomycins I, J, X, and Z, but accumulated the nucleoside moieties nikkomycins C-X and C-Z. The mutant was complemented to nikkomycin production (I, J, X, Z ) by nikC expressed from the mel promoter of the vector pIJ702. Furthe rmore, the nikkomycin-negative phenotype was reversed by the addition of picolinic acid, a precursor of the peptidyl moiety of nikkomycins ( nikkomycin D), into the culture medium. The nikC gene was expressed in Escherichia coil and identified and characterized at the enzyme level . NikC encodes an L-lysine 2-aminotransferase, and the activity was ex clusively detected in nikkomycin producers and its presence correlated to nikkomycin production. The nikC-inactivated mutant grew with L-lys ine as sole source of nitrogen and carbon, indicating that L-lysine 2- aminotransferase is not required for lysine catabolism. Our results id entified the nikC-encoded L-lysine 2-aminotransferase as the nikkomyci n biosynthetic enzyme that catalyzes the initial reaction in nikkomyci n D biosynthesis. The NikC protein belongs to a novel family of pyrido xamine or pyridoxal-phosphate-dependent dehydrases and aminotransferas es, some of which are involved in dideoxy- and deoxy-aminosugar biosyn thesis.