PMC

(a) Hypothetical prodigiosin (1) biosynthetic pathway in P. rubra (by analogy to the pathway elucidated in Serratia) and the cyclization of 1 into cycloprodigiosin (2) investigated in this work. (b) Comparison of the pig gene cluster in Serratia, which produces only 1, and P. rubra, which produces both 1 and 2, shows that pigN is absent in the latter. The gene downstream of pigM in P. rubra shows no similarity to pigN. Also shown is an excerpt of P. rubra contig 4, which contains PRUB675 and PRUB680. Genes in pink have homology to Serratia pig genes and/or to Streptomyces red genes. (c) The Rieske monooxygenase-like RedG catalyzes the carbocyclization of undecylprodigiosin to form streptorubin B, motivating our search for the enzyme responsible for the analogous cyclization of 1 in P. rubra.

(a) In vivo production of prodiginines. For experiments in E. coli, the cells were fed MBC (4), which is turned into prodigiosin (1) by PigBCDE. 1 is in turn converted to cycloprodigiosin (2) by PRUB680 if present. For standards, see . (b) In vitro experiments with PRUB680 in inverted E. coli membrane vesicles. Vesicles were shaken with 10 μM 1 in the presence of the indicated cofactors (left). Reactions were initiated by addition of 250 μM reducing cofactor. For metal dependency experiments (right), vesicles were incubated with 4 mM EDTA, followed by 5 mM metal ion, before initiating the reaction with 250 μM (6R)-tetrahydrobiopterin. Error bars represent s.d. of triplicates.