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Life As We (Don't) Know It

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.

9 comments on “Arsenic Life No More”

  1. petros says:

    Note the comments from the author of the original paper showing that she still believes in what she published!

  2. Jose says:

    Yes Petros, saw the same thing. Nothing short of staggering… and she got picked up at LBNL? Even more staggering. And the damn paper hasn’t been retracted??!!

  3. Anonymous says:

    Her naming scheme for GFAJ-1 worked (Give Felisa a Job) — she has a job. She’s likely more famous and recognized than I could ever hope to be, despite cranking away with fairly successful projects. She was invited to give a TED talk. She has incredible number of hits on Google and a Wikipedia page.
    She won, science lost. This is the result of science by press release instead of traditional channels.
    Secretly though, I would probably do exactly what she did if I were presented with the opportunity. I’m sure she thought her data was sufficient at the time. Even if I had a time machine that would let me see that my data wouldn’t survive more rigorous testing, I think I would have still gone ahead and released the press release.
    What would her (or my hypothetical) career would have been like without that press release? Just another struggling post-doc in a sea of others.

  4. Anonymous Academic says:

    @2: She was hired by John Tainer (structural biologist, joint with Scripps) – according to one of the articles I read, she’s now trying to crystallize ribosomes from GFAJ-1 in the hope of finding arsenate in RNA.

  5. “She’s now trying to crystallize ribosomes from GFAJ-1 in the hope of finding arsenate in RNA.”
    Well, since she hasn’t done it before I am sure she thinks it’s worth doing. According to the story told by Chembark on his blog, that’s what she thinks about organic synthesis in any case.

  6. Andy says:

    Ok, I get that the rate of spontaneous hydroylsis of an arsenodiester linkage is measured as 10^17 fold faster than the rate of hydrolysis of a phosphodiester linkage, but WHY is that so?

  7. Provocateur says:

    #3 ….
    I agree.Such a sad but honest assessment.
    And I tht honesty was valued in science.
    I still would not do it the way she did becos it
    Makes me extremely uncomfortable.
    But ppl like me are fighting against Darwinism

  8. Yancey Ward says:

    I will assume she had good faith belief in the initial results. However, hanging on to the bitter end is going come at a high price eventually.

  9. sepisp says:

    #6: The general explanation is a periodic trend: larger atoms of the heavier elements have a more diffuse electron cloud. The charge of the nucleus is screened by the lower shells, and the nucleus is farther away from the valence shell. Consequently, the electron cloud is more polarizable, and will in a way “autocatalyze” its own hydrolysis reactions. I’m sure quantum chemists have a quantitative explanation also.

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