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Function

Burkholderia species produce oxalate which helps maintain environmental pH. Two enzymes are required to produce oxalate, ObcA and ObcB. ObcA catalyzes first, resulting in a tetrahedral C6-CoA adduct from acetyl-CoA and oxaloacetate. ObcB then produces three products from the C6-CoA adduct which include oxalate, acetoacetate, and CoA. In Burkholderia thailandensis and Burkholderia pseudomallei Obc1 carries out both steps of this reaction as it is a single bi-functional enzyme ().

Disease

Burkholderia species have many pathogenic consequences for plants and humans. B. cepacia effects immunocompromised individuals that may have cystic fibrosis or chronic granulomatous disease. B. pseudomallei causes a lethal infection called melioidosis that results in formation of abscesses. In plants, B. glumae causes bacterial panicle blight in rice.

Relevance

Understanding the reaction that is catalyzed by ObcA and ObcB in two steps and Obc1 in one step has clinical relevance. Currently, the molecular basis of the Obc enzymes is unknown. By studying these enzymes, a treatment may be developed for disease control that is caused by Obc enzymes.

Structural highlights

Secondary structures of Obc1 include alpha helices, beta sheets, random coil, and turns. The most abundant secondary structure is alpha helices followed by beta sheets and random coil, with turns being the least abundant (). Obc1 consists of two domains, an N-domain and C-domain that is composed of two regions: A cap region and an alpha/beta hydrolase fold(). A space-filling view of a protein shows how much space the atoms take up in the protein. The space-fill view of Obc1 shows that the atoms in this protein consume a considerable amount of space as there are no gaps in the protein (). Obc1 is composed of equal, dispersed amounts of hydrophobic and hydrophilic patches(). Important features of the ligand glycerol include that it is hydrophilic. This is demonstrated by the hydrogen bonds it creates in the active site (). The catalytic triad helps the protein achieve its function by making Ser-935 act in a nucleophilic attack to generate a tetrahedral intermediate, which is the first step in producing oxalate(). The catalytic triad consists of S935, D997, and H1069. Amino acids that make up the active site include S785, T786, P787, R856, H934, S936, F974, R999, D1061, D1067, S1070, and R1073 ().