Structural Insights into Oxalate Biosynthetic Component

Abstract

Bacterial quorum sensing (QS), a cell‐to‐cell communication process in many Proteobacteria, controls the gene expression for bacterial population‐wide characteristics, including bioluminescence, motility, and virulence‐related factors. Recently, QS has been recognized to provide further benefits at the population level by regulating the production of public goods, the function of which could be beneficial to all members of the group. In Burkholderia species, oxalic acid was recently identified as an excreted public good for the QS‐dependent growth. In these species, QS‐mediated oxalogenesis via the oxalate biosynthetic component (obc) is a cellular event indispensable for the survival of bacteria in the stationary phase. In B. glumae, obc consists of two genes encoding ObcA and ObcB for coordinating the production of oxalic acid, as well as acetoacetate and CoA, by using oxaloacetate and acetyl‐CoA as substrates. Unlike B. glumae, there is a bi‐functional enzyme Obc1 from B. thailandensis. Sequence analysis indicates that Obc1 has an ObcA‐like N‐terminal domain and shows ObcB activity in its C‐terminal domain despite no sequence homology with ObcB. We will present our recent progress on structural and functional analyses of ObcA and Obc1. In ObcA, oxaloacetate serves as a nucleophile by forming an enolate intermediate mediated by Tyr322 as a general base, which then attacks the thioester carbonyl carbon of acetyl‐CoA to yield a tetrahedral adduct between the two substrates. Therefore, ObcA catalyzes its reaction by combining the enolase and acetyltransferase superfamilies, but the presence of the metal‐coordination shell and absence of general acid(s) likely produces an unusual tetrahedral CoA adduct as a stable product. In Obc1, the C‐terminal domain has an α/β hydrolase fold that has a catalytic triad for oxalate production and a novel oxyanion hole distinct from the canonical HGGG motif in other α/β hydrolases. Functional analyses through mutagenesis studies suggested that His‐934 is an additional catalytic acid/base for its lyase activity and liberates two additional products, acetoacetate and CoA. These results provide structural and functional insights into bacterial oxalogenesis.Support or Funding InformationThis work was supported by Next Generation BioGreen 21 program of Rural Development Administration (Plant Molecular Breeding Center) of Republic of KOREA.