Improvement of nikkomycin production by enhanced copy of sanU and sanV in Streptomyces ansochromogenes and characterization of a novel glutamate mutase encoded by sanU and sanV

Abstract

Previous studies revealed that two genes- sanU and sanV were associated with nikkomycin biosynthesis in Streptomyces ansochromogenes. A plasmid used to increase an extra copy of sanU and sanV was constructed and introduced into wild-type strain. HPLC results showed that nikkomycin production of recombinant strain was about 1.8 fold than that of wild-type strain. RT-PCR analysis indicated that the transcriptional level of sanU and sanV in this recombinant strain was about two folds than that of wild-type strain. The sanU and sanV were expressed in E. coli BL21 (DE3). SanU and SanV were purified individually. SanU and SanV assembled with coenzyme B 12 to form a complete enzyme in vitro, which showed glutamate mutase activity. The glutamate mutase converted l-glutamate to l-threo- β -Methylaspartic acid, and then l-threo- β -Methylaspartic acid was probably deaminated to form 2-oxo-3-methylsuccinic acid to join biosynthetic pathway of the peptidyl moiety HPHT in S. ansochromogenes. SanU is the coenzyme B 12-binding component and more than two folds of SanU are required for maximal enzyme activity. The optimal pH and temperature for the formed enzyme are 7.5–8.5 and 35–42 °C, respectively. Sulfhydryl compounds are important for activity of the reassembled enzyme.