Abstract
Bdellovibrio bacteriovorus is an unusual δ-proteobacterium that invades and preys on other Gram-negative bacteria and is of potential interest as a whole cell therapeutic against pathogens of man, animals and crops. PTPs (protein tyrosine phosphatases) are an important class of enzyme involved in desphosphorylating a variety of substrates, often with implications in cell signaling. The B. bacteriovorus open reading frame Bd1204 is predicted to encode a PTP of unknown function. Bd1204 is both structurally and mechanistically related to the PTP-like phytase (PTPLP) class of enzymes and possesses a number of unique properties not observed in any other PTPLPs characterized to date. Bd1204 does not display catalytic activity against some common protein tyrosine phosphatase substrates but is highly specific for hydrolysis of phosphomonoester bonds of inositol hexakisphosphate. The structure reveals that Bd1204 has the smallest and least electropositive active site of all characterized PTPLPs to date yet possesses a unique substrate specificity characterized by a strict preference for inositol hexakisphosphate. These two active site features are believed to be the most significant contributors to the specificity of phytate degrading enzymes. We speculate that Bd1204 may be involved in phosphate acquisition outside of prey.
Highlights
Phytases are a group of enzymes that catalyze the release of orthophosphate from Inositol hexakisphosphate (InsP6) [1]
There are four classes of phytases that have been characterized to date, including the histidine acid phosphatases (HAP), b-propeller phytase (BPP), purple acid phosphatases, and the protein tyrosine phosphatase-like phytases (PTPLPs), known as cysteine phytases [1,2,3]
An examination of the phytase diversity within microbial genomes and environmental metagenomes revealed that the BPP class plays a major role in phytate degradation in aquatic environments whereas HAPs were predominant in enteric bacteria and plant pathogens [4]
Summary
Phytases are a group of enzymes that catalyze the release of orthophosphate from Inositol hexakisphosphate (InsP6) [1]. Proteins belonging to the PTPLP superfamily have been identified in the plant pathogens Pseudomonas syringae and Xanthomonas campestris, mammalian pathogens Clostridium botulinum and Legionella pneumophila, the myxobacterium Stigmatella aurentiaca and the predatory bacterium Bdellovibrio bacteriovorus. The latter are predatory bacteria that penetrate the periplasmic space of other Gram-negative bacteria, metabolizing the cytoplasmic and periplasmic contents of prey from within before reproducing and eventually lysing the prey cell [6]. The presence of a PTPLP encoding gene in B. bacteriovorus raised interesting questions about the possible role of this enzyme in the biology of this predatory species, since InsP6 is more likely to be encountered outside of prey in the environment [7]
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