The molecular regulation of the reductive pentose phosphate pathway in Proteobacteria and Cyanobacteria

Abstract

In phototrophic and chemoautotrophic proteobacteria, genes encoding enzymes of the Calvin-Benson-Bassham pathway of CO2 fixation are often found in clusters that are transcribed from a single promoter under control of the LysR-type transcriptional activator, CbbR. Mutations affecting CbbR prevent induction of cbb genes. Gel-retardation assays have demonstrated CbbR binding to putative regulatory regions of cbb operons, and in two cases, footprinting experiments have delimited the nucleotide sequence protected by CbbR. Fusion of cbb control sequences to reporter genes has allowed the regions required for promoter activity to be defined, and recent experiments indicate that the cbb regulon in Rhodobacter is controlled by a global two-component signal transduction system that also regulates other metabolic processes in this organism. Different ways of regulating CBB cycle enzymes that also have roles in heterotrophic metabolism have recently been discovered. In cyanobacteria, the genes of the CBB pathway are organized and regulated differently, and these oxygen-evolving phototrophic bacteria have evolved different strategies to control the assimilation of CO2.

Ribulose bisphosphate carboxylase activity and a Calvin cycle gene cluster in Sulfobacillus species

“…The number and order of genes in CBB cycle operons in bacteria vary considerably (Gibson & Tabita, 1996;Kusian & Bowien, 1997). The inferred products of eight potential cbb genes found in a cluster in S. acidophilus have the key residues required for activity.…”

“…The cluster was not preceded by a cbbR gene, which is upstream of cbb gene clusters in many autotrophic proteobacteria and encodes a LysR-type transcriptional regulator of the cbb genes (Gibson & Tabita, 1996;Kusian & Bowien, 1997). The upstream genes encoded a putative RNA polymerase factor sigma70 (orf1) and PEP carboxylase (ppc) and those downstream of the cluster encoded a putative acetyltransferase (orf2), a sensor histidine kinase (orf3) and response regulator receiver (orf4), and a transcription terminator factor Rho (orf5).…”

Metabolic Signals That Lead to Control of CBB Gene Expression in Rhodobacter capsulatus

“…Thus, when carbon substrates such as L-malate and succinate are metabolized, the CBB cycle facilitates balancing of the oxidation-reduction potential (redox poise) of the cell (17,37,69). Given its different roles in photoheterotrophic and photoautotrophic metabolism, it is not surprising that multiple levels of control influence expression of the CBB system (10,22,46,59,67).Enzymes of the CBB pathway are encoded by the cbb genes, which are organized in regulons in both Rhodobacter capsulatus (44, 45) and Rhodobacter sphaeroides (19,23,24). For both organisms, there are two major cbb operons: the form I (cbb I ) operon, containing form I RubisCO genes (cbbL cbbS), is predominant under autotrophic growth conditions, and the form II (cbb II ) operon, containing the form II RubisCO gene (cbbM), is expressed under all growth conditions, albeit at enhanced levels during autotrophic growth.…”

Maximum activity of recombinant ribulose 1,5-bisphosphate carboxylase/oxygenase of Anabaena sp. strain CA requires the product of the rbcX gene

“…Unlike the form II enzyme, the form I RubisCO is also comprised of a second polypeptide, the small subunit. In cyanobacteria, the large and small subunits are encoded by the rbcL and rbcS genes, respectively, while in proteobacteria, these proteins are encoded by the cbbL and cbbS genes, which often are found associated with many additional structural and regulatory genes of the Calvin-BensonBassham pathway (8). Recently it was found that the genes in and around the rbcL and rbcS genes of three species of Anabaena are organized differently from the corresponding genes in other cyanobacteria (15,16).…”