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 biosynthesis 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. Furthermore, 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 coli and identified and characterized at the enzyme level. NikC encodes an L-lysine 2-aminotransferase, and the activity was exclusively detected in nikkomycin producers and its presence correlated to nikkomycin production. The nikC-inactivated mutant grew with L-lysine as sole source of nitrogen and carbon, indicating that L-lysine 2-aminotransferase is not required for lysine catabolism. Our results identified the nikC-encoded L-lysine 2-aminotransferase as the nikkomycin biosynthetic enzyme that catalyzes the initial reaction in nikkomycin D biosynthesis. The NikC protein belongs to a novel family of pyridoxamine or pyridoxal-phosphate-dependent dehydrases and aminotransferases, some of which are involved in dideoxy- and deoxy-aminosugar biosynthesis.