Hydroxyquinone O-methylation in mitomycin biosynthesis.
Mitomycins are bioreductively activated DNA-alkylating agents. One member of this family, mitomycin C, is in clinical use as part of combination therapy for certain solid tumors. The cytotoxicity displayed by mitomycins is dependent on their electrochemical potential which, in turn, is governed in part by the substituents of the quinone moiety. In this paper we describe studies on the biogenesis of the quinone methoxy group present in mitomycins A and B. An engineered Streptomyces lavendulae strain in which the mmcR methyltransferase gene had been deleted failed to produce the three mitomycins (A, B, and C) that are typically isolated from the wild type organism. Analysis of the culture extracts from the mmcR-deletion mutant strain revealed that two new metabolites, 7-demethylmitomycin A and 7-demethylmitomycin B, had accumulated instead. Production of mitomycins A and C or mitomycin B was selectively restored upon supplementing the culture medium of a S. lavendulae strain unable to produce the key precursor 3-amino-5-hydroxybenzoate with either 7-demethylmitomycin A or 7-demethylmitomycin B, respectively. MmcR methyltransferase obtained by cloning and overexpression of the corresponding mmcR gene was shown to catalyze the 7-O-methylation of both C9beta- and C9alpha-configured 7-hydroxymitomycins in vitro. This study provides direct evidence for the catalytic role of MmcR in formation of the 7-OMe group that is characteristic of mitomycins A and B and demonstrates the prerequisite of 7-O-methylation for the production of the clinical agent mitomycin C.
Grüschow
Sabine
S
Life Sciences Institute, Department of Medicinal Chemistry, University of Michigan, Ann Arbor, MI 48109, USA.
Chang
Leng-Chee
LC
Mao
Yingqing
Y
Sherman
David H
DH
D002384:Catalysis; D008745:Methylation; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism; D008937:Mitomycins / Q000096:biosynthesis* / Q000737:chemistry*; D015394:Molecular Structure; D009154:Mutation / Q000235:genetics; D013302:Streptomyces / Q000235:genetics / Q000378:metabolism
D008937:Mitomycins; C046000:mitomycin A; D008780:Methyltransferases