Inactivation of Mg chelatase during transition from anaerobic to aerobic growth in Rhodobacter capsulatus

Robert D. Willows, Vanessa Lake, Thomas Hugh Roberts, Samuel I. Beale*

*Corresponding author for this work

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

The facultative photosynthetic bacterium Rhodobacter capsulatus can adapt from an anaerobic photosynthetic mode of growth to aerobic heterotrophic metabolism. As this adaptation occurs, the cells must rapidly halt bacteriochlorophyll synthesis to prevent phototoxic tetrapyrroles from accumulating, while still allowing heme synthesis to continue. A likely control point is Mg chelatase, the enzyme that diverts protoporphyrin IX from heme biosynthesis toward the bacteriochlorophyll biosynthetic pathway by inserting Mg2+ to form Mgprotoporphyrin IX. Mg chelatase is composed of three subunits that are encoded by the bchI, bchD, and bchH genes in R. capsulatus. We report that BchH is the rate-limiting component of Mg chelatase activity in cell extracts. BchH binds protoporphyrin IX, and BchH that has been expressed and purified from Escherichia coli is red in color due to the bound protoporphyrin IX. Recombinant BchH is rapidly inactivated by light in the presence of O2, and the inactivation results in the formation of a covalent adduct between the protein and the bound protoporphyrin IX. When photosynthetically growing R. capsulatus cells are transferred to aerobic conditions, Mg chelatase is rapidly inactivated, and BchH is the component that is most rapidly inactivated in vivo when cells are exposed to aerobic conditions. The light- and O2-stimulated inactivation of BchH could account for the rapid inactivation of Mg chelatase in vivo and provide a mechanism for inhibiting the synthesis of bacteriochlorophyll during adaptation of photosynthetically grown cells to aerobic conditions while still allowing heme synthesis to occur for aerobic respiration.

Original languageEnglish
Pages (from-to)3249-3258
Number of pages10
JournalJournal of Bacteriology
Volume185
Issue number11
DOIs
Publication statusPublished - Jun 2003

Fingerprint Dive into the research topics of 'Inactivation of Mg chelatase during transition from anaerobic to aerobic growth in Rhodobacter capsulatus'. Together they form a unique fingerprint.

Cite this