Crystal structure of RebC, a flavoprotein involved in rebeccamycin biosynthesis.

Rebeccamycin, an antitumor compound, is synthesized by L. aerocolonigenes from the precursor L-tryptophan [Biosci. Biotechnol. Biochem. (2003) 67: 127-38]. One step in the biosynthetic pathway involves the net eight-electron oxidation of chlorinated chromopyrrolic acid to generate the rebeccamycin aglycone, which is carried out by the enzymatic pair, RebP and RebC [PNAS (2005) 102: 461-6]. Substitution of RebC with StaC -- a homologue with 65% identity to RebC -- results in the production of the staurosporine aglycone in lieu of the rebeccamycin aglycone [JACS (2006) 128: 12289-98]. While both RebC and StaC are annotated as flavin monooxygenases, only RebC is able to bind flavin adenine dinucleotide [JACS (2006) 128: 12289-98]. The structure of RebC bound to flavin adenine dinucleotide (FAD) was recently solved with 1.8A resolution using phases from a samarium derivative. The structure of RebC bears much resemblance to phenol hydroxylase, a flavin-dependent monooxygenase. This suggests that RebC is also a flavin-dependent monooxygenase, which might react with a yet-unidentified product produced by RebP. Residues in the structure near FAD are potentially responsible for the differences in FAD-binding and activity found between RebC and StaC. We are using the crystal structure as a guide to investigate the properties of various RebC mutants, in hope of determining the structural basis for enzyme specificity. [ABSTRACT FROM AUTHOR]