Department of Microbiology, The Ohio State University, 484 West 12th Avenue, Columbus, OH 43210-1292, USA.
J Bacteriol. 2010 Mar;192(5):1324-31. doi: 10.1128/JB.01442-09. Epub 2009 Dec 28.
Ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) catalyzes the assimilation of atmospheric CO(2) into organic matter and is thus central to the existence of life on earth. The beginning of the 2000s was marked by the discovery of a new family of proteins, the RubisCO-like proteins (RLPs), which are structural homologs of RubisCO. RLPs are unable to catalyze CO(2) fixation. The RLPs from Chlorobaculum tepidum, Bacillus subtilis, Geobacillus kaustophilus, and Microcystis aeruginosa have been shown to participate in sulfur metabolism. Whereas the precise function of C. tepidum RLP is unknown, the B. subtilis, G. kaustophilus, and M. aeruginosa RLPs function as tautomerases/enolases in a methionine salvage pathway (MSP). Here, we show that the form II RubisCO enzyme from the nonsulfur purple bacterium Rhodospirillum rubrum is also able to function as an enolase in vivo as part of an MSP, but only under anaerobic conditions. However, unlike B. subtilis RLP, R. rubrum RLP does not catalyze the enolization of 2,3-diketo-5-methylthiopentyl-1-phosphate. Instead, under aerobic growth conditions, R. rubrum RLP employs another intermediate of the MSP, 5-methylthioribulose-1-phosphate, as a substrate, resulting in the formation of different products. To further determine the interrelationship between RubisCOs and RLPs (and the potential integration of cellular carbon and sulfur metabolism), the functional roles of both RubisCO and RLP have been examined in vivo via the use of specific knockout strains and complementation studies of R. rubrum. The presence of functional, yet separate, MSPs in R. rubrum under both aerobic (chemoheterotrophic) and anaerobic (photoheterotrophic) growth conditions has not been observed previously in any organism. Moreover, the aerobic and anaerobic sulfur salvage pathways appear to be differentially controlled, with novel and previously undescribed steps apparent for sulfur salvage in this organism.
核酮糖-1,5-二磷酸羧化酶/加氧酶（RubisCO）催化大气 CO2 同化为有机物质，因此是地球上生命存在的核心。21 世纪初的标志是发现了一类新的蛋白质，即 RubisCO 样蛋白（RLP），它是 RubisCO 的结构同源物。RLP 不能催化 CO2 固定。已经证明来自嗜热杆菌、枯草芽孢杆菌、产硷杆菌和铜绿微囊藻的 RLPs 参与硫代谢。虽然 C. tepidum RLP 的精确功能未知，但枯草芽孢杆菌、产硷杆菌和铜绿微囊藻的 RLPs 在甲硫氨酸挽救途径（MSP）中作为互变异构酶/烯醇酶发挥作用。在这里，我们表明非硫紫色细菌 Rhodospirillum rubrum 的 II 型 RubisCO 酶也能够作为 MSP 的一部分在体内作为烯醇酶发挥作用，但仅在厌氧条件下。然而，与枯草芽孢杆菌 RLP 不同，R. rubrum RLP 不能催化 2,3-二酮-5-甲基硫代戊基-1-磷酸的烯醇化。相反，在好氧生长条件下，R. rubrum RLP 将 MSP 的另一个中间产物 5-甲基硫代核糖-1-磷酸作为底物，导致形成不同的产物。为了进一步确定 RubisCO 和 RLP 之间的相互关系（以及细胞碳和硫代谢的潜在整合），通过使用特定的敲除菌株和 Rhodospirillum 的互补研究，在体内检查了 RubisCO 和 RLP 的功能作用。在任何生物体中，以前都没有观察到在好氧（化能异养）和厌氧（光异养）生长条件下，R. rubrum 中存在功能上独立的 MSP。此外，好氧和厌氧的硫挽救途径似乎受到不同的控制，在该生物体中，硫挽救出现了新的和以前未描述的步骤。
