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October 8, 2012
Arsenic Life No More
The "arsenic life" bacterium has taken a number of blows in the scientific literature, and now it's taken another. A close look at its phosphate uptake system shows that these proteins in the GFAJ-1 bacteria not selective for arsenate (or at least tolerant of it, compared to normal lines). They are, in fact, extremely selective for phosphate.
All of the proteins can discriminate at least 500-fold over arsenate, but one of them from GFAJ-1 (highly expressed under the arsenate conditions) is 4,500-fold selective. The authors show, via X-ray crystallography, what sort of mutations hae occurred to give the binding site such high selectivity, which lead to the (slightly larger) arsenate disturbing a key hydrogen bond. This is what you'd expect if these bacteria were, in fact, still phosphate-dependent and needed to extract every bit of it they could from their arsenate-rich environment.
Here's a summary at Nature News. I believe that we can now declare this particular idea dead - everything is pointing the other way.
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