Investigation of the biosynthesis of the pipecolate moiety of neuroprotective polyketide meridamycin.

Biogenesis of the pipecolate moiety of neuroprotective agent meridamycin in Streptomyces sp. NRRL30748 was investigated in feeding studies using lysine specifically labeled with (15)N at the α-amino or the ε-amino nitrogen position. Fourier transform mass spectrometry analysis with ultra-high mass resolving power and accurate mass measurement capability was employed to resolve the (15)N peak of labeled meridamycin from the (13)C peak of unlabeled meridamycin, allowing the precise calculation of labeling contents under each condition. The relative enrichment of (15)N-labeled meridamycin was ~43% with L-[α-(15)N]-lysine feeding and ~14% with L-[α-(15)N]-lysine feeding, suggesting two distinguishable pathways, with concomitant loss of either the ε-amino group or the α-amino group of lysine, were involved in the generation of the pipecolate moiety of meridamycin in this bacterium. PCR cloning using degenerate primers identified a proC gene encoding a putative pyrroline-5-carboxylate reductase, which was expected to catalyze the conversion of piperideine-6-carboxylate to pipecolate. However, inactivation of this locus did not significantly affect the incorporation of α-(15)N- or ε-(15)N-labeled lysine into meridamycin, indicating the existence of an alternative route for the last step of the lysine ε-transamination pathway. This work revealed the diversity and complexity of the biosynthetic pathways for pipecolate synthesis in the meridamycin producing bacterium Streptomyces sp. NRRL30748.