Novel inositol catabolic pathway in T hermotoga maritima

Abstract

Summary myo ‐ inositol ( MI ) is a key sugar alcohol component of various metabolites, e.g. phosphatidylinositol‐based phospholipids that are abundant in animal and plant cells. The seven‐step pathway of MI degradation was previously characterized in various soil bacteria including B acillus subtilis . Through a combination of bioinformatics and experimental techniques we identified a novel variant of the MI catabolic pathway in the marine hyperthermophilic bacterium T hermotoga maritima . By using in vitro biochemical assays with purified recombinant proteins we characterized four inositol catabolic enzymes encoded in the TM 0412– TM 0416 chromosomal gene cluster. The novel catabolic pathway in T . maritima starts as the conventional route using the myo ‐inositol dehydrogenase IolG followed by three novel reactions. The first 2‐keto‐ myo ‐inositol intermediate is oxidized by another, previously unknown NAD ‐dependent dehydrogenase TM 0412 (named IolM ), and a yet unidentified product of this reaction is further hydrolysed by TM 0413 ( IolN ) to form 5‐keto‐ l ‐gluconate. The fourth step involves epimerization of 5‐keto‐ l ‐gluconate to d ‐tagaturonate by TM 0416 ( IolO ). T. maritima is unable to grow on myo ‐inositol as a single carbon source. The determined in vitro specificity of the InoEFGK ( TM 0418– TM 0421) transporter to myo ‐inositol‐phosphate suggests that the novel pathway in T hermotoga utilizes a phosphorylated derivative of inositol.

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