The Tetrapyrrole Biosynthetic Pathway and Its Regulation in Rhodobacter capsulatus

Abstract

The purple anoxygenic photosynthetic bacterium Rhodobacter capsulatus is capable of growing in aerobic or anaerobic conditions, in the dark or using light, etc. Achieving versatile metabolic adaptations from respiration to photosynthesis requires the use of tetrapyrroles such as heme and bacteriochlorophyll, in order to carry oxygen, to transfer electrons and to harvest light energy. A third tetrapyrrole, cobalamin (vitamin B12), is synthesized and used as a cofactor for many enzymes. Heme, bacteriochlorophyll and vitamin B12 constitute three major end products of the tetrapyrrole biosynthetic pathway in purple bacteria. Their respective synthesis involves a plethora of enzymes several that have been characterized and several that are uncharacterized as described in this review. To respond to changes in metabolic requirements the pathway undergoes complex regulation to direct the flow of tetrapyrrole intermediates into a specific branch(s) at the expense other branches of the pathway. Transcriptional regulation of the tetrapyrrole synthesizing enzymes by redox conditions and pathway intermediates is reviewed. In addition, we discus the involvement of several transcription factors (RegA, CrtJ, FnrL, AerR, HbrL, Irr) as well as the role of riboswitches. Finally, the interdependence of the tetrapyrrole branches on each others synthesis is discussed.

Temporal metatranscriptomic patterning in phototrophic Chloroflexi inhabiting a microbial mat in a geothermal spring

“…Although this expression of genes for the enzymes of BChl biosynthesis under anoxic conditions is consistent with the laboratory studies for C. aurantiacus (Oelze, 1992) and anoxygenic phototrophic proteobacteria (Ponnampalam et al, 1995;Gregor and Klug, 1999;Zappa et al, 2010), the Chloroflexus spp. and Roseiflexus spp.…”

Elucidation of roles for vitamin B 12 in regulation of folate, ubiquinone, and methionine metabolism

“…Allosteric control of HemE would provide Halomonas a means by which to control flux through these pathways based on B 12 availability, and suggests a fundamentally new role for B 12 in cellular metabolism. Prior reports on control of the tetrapyrrole biosynthetic pathway in other microbes have identified regulatory feedback controls by B 12 -dependent riboswitches (27) and redox signaling cascades (28). Taking these data together, we find that vitamin B 12 regulation of these steps could result in redirection of metabolism between biosynthesis of heme versus B 12 biosynthesis.…”

Prokaryotic Heme Biosynthesis: Multiple Pathways to a Common Essential Product

“…Short reviews within otherwise focused manuscripts can be found (35)(36)(37)(38)(39), and there is an excellent review of tetrapyrrole biosynthesis in Rhodobacter capsulatus (40). The last broad-scope genome-based review of prokaryotic heme synthesis was reported over a dozen years ago by O'Brian and Thony-Meyer (41).…”