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Biological Chemistry

Bacterial Protein Outwits Arsenate

Hydrogen bond drives preference for phosphate, with implications for arsenic-based life saga

by Carmen Drahl
October 8, 2012 | APPEARED IN VOLUME 90, ISSUE 41

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Credit: Nature
When binding to arsenate (at bottom), a key hydrogen bond in P. fluorescens periplasmic phosphate-binding protein deviates from the 180° norm (at top).
09041-scicon-phosphate.jpg
Credit: Nature
When binding to arsenate (at bottom), a key hydrogen bond in P. fluorescens periplasmic phosphate-binding protein deviates from the 180° norm (at top).

A distorted hydrogen bond shapes how a bacterial protein distinguishes essential phosphate from toxic arsenate, researchers report (Nature, DOI: 10.1038/nature11517). The work represents another nail in the coffin for the controversial claim that a microbe called GFAJ-1 can incorporate arsenate in its metabolites. Wondering how life evolved to deal with arsenate-rich environments, Weizmann Institute of Science postdoc Mikael Elias, Dan S. Tawfik, and colleagues turned to periplasmic phosphate-binding proteins, which regulate passage of phosphate anions through microbes’ inner membranes. They now find that versions of this protein from several bacteria, including GFAJ-1, are highly selective for phosphate. X-ray structures of the protein, from the bacterium Pseudomonas fluorescens, reveal that when arsenate binds, a hydrogen bond to an aspartic acid residue becomes distorted. Mutating the residue makes the protein less choosy for phosphate over arsenate, reinforcing the idea that the distortion drives the protein’s phosphate selectivity. Tawfik thinks that mechanism is also at play in the analogous protein from GFAJ-1, allowing it to survive in arsenate-rich environments. Scripps Research Institute biochemist Gerald F. Joyce says GFAJ-1 likely has multiple adaptations: “Now can we all stop talking about ‘arsenic-based life’?”

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