Biocurious

/ a biophysics blog

Molecule of the Month: Selenocysteine Synthase

Posted 9 August 2008 by PhilipJ under

[sorry for the lack of updates, I was on vacation!]

Selenocysteine Synthase

If you have visited your local health food store or looked closely at the ingredients in your daily multivitamin, you may have noticed that the element selenium is often listed as one of the beneficial supplements. Selenium is a double-edged sword, however. In general, selenium compounds are toxic and have an unpleasant garlicy odor, but in trace amounts, selenium is essential for our health. Selenium atoms are similar to sulfur atoms, with similar properties, except that selenium compounds tend to be more reactive. In a few specialized proteins, this extra reactivity is just what is needed. For instance, by using a selenium atom instead of sulfur, thioredoxin reductase improves its rate of catalysis by 100 times, and formate dehydrogenases act 300 times faster.

Proteins contain two types of amino acids with sulfur atoms, and both may be made in versions with selenium atoms. Selenomethionine is not made specifically by cells, but it is created occasionally by accident by the normal enzymes that make methionine. This is not a problem, however, since it is similar enough to normal methionine. It is, however, very useful to crystallographers to help with the determination of x-ray crystal structures, since it has more electrons than sulfur and is easily located in x-ray experiments. Selenocysteine, on the other hand, is more reactive than normal cysteine, and it is specifically added to special selenoproteins when it is needed.

More from David Goodsell here.

  

  1. ponderingfool    21 August 08    #

    If I am not mistaken it is also called O-phosphoseryl-tRNA:selenocysteinyl-tRNA synthase (SepSecS for short).

    The structure of the archaeal homolog was published online 4 days after the eukaryotic one.

    archaeal
    http://nar.oxfordjournals.org/cgi/content/full/36/4/1187

    eukaryotic
    http://www.jbc.org/cgi/content/full/283/9/5849

    What it gets called depends it appears on which lab is writing the paper. The first paper came from the Soll lab in which they called it SepSecS.
    http://www.pnas.org/content/103/50/18923.abstract

    25 days later Hatfield published in which they named it selenocysteine synthase (SecS).
    http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050004&ct=1

    Of course the bacterial selenocysteine synthase (SelA) is a different enzyme which can make the Hatfield nomenclature for the archaeal/eukaryotic enzyme confusing though it is simpler than the lengthy name the Soll lab gave it.

    Just what we need another enzyme called different things depending on which lab is writing about it.

    Scientific politics, isn’t it fun?


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