Promiscuity of Exiguobacterium sp. AT1b o-succinylbenzoate synthase illustrates evolutionary transitions in the OSBS family

[Display omitted] •Evolution is thought to proceed through promiscuous intermediates.•The NSAR/OSBS subfamily includes catalytically promiscuous proteins.•The biological function of the NSAR/OSBS from Exiguobacterium sp. AT1b is OSBS.•Exiguobacterium OSBS catalyzes NSAR as a promiscuous, non-biologi...

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Veröffentlicht in:Biochemical and biophysical research communications 2014-07, Vol.450 (1), p.679-684
Hauptverfasser: Brizendine, Ashley M., Odokonyero, Denis, McMillan, Andrew W., Zhu, Mingzhao, Hull, Ken, Romo, Daniel, Glasner, Margaret E.
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Sprache:eng
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Zusammenfassung:[Display omitted] •Evolution is thought to proceed through promiscuous intermediates.•The NSAR/OSBS subfamily includes catalytically promiscuous proteins.•The biological function of the NSAR/OSBS from Exiguobacterium sp. AT1b is OSBS.•Exiguobacterium OSBS catalyzes NSAR as a promiscuous, non-biological reaction.•Promiscuous NSAR activity was present before NSAR evolved into biological function. Catalytic promiscuity, which is the ability to catalyze more than one reaction in the same active site, is thought to facilitate the evolution of new protein functions. Although many enzymes are catalytically promiscuous, there is little direct evidence to show how promiscuous activities evolved into biological functions. We are seeking evidence for this model by studying the o-succinylbenzoate synthase (OSBS) family. Most enzymes within this family only catalyze OSBS, which is a step in menaquinone synthesis. However, several characterized enzymes in one branch of the family (called the NSAR/OSBS subfamily) efficiently catalyze both OSBS and N-succinylamino acid racemization (NSAR). Based on genome context, NSAR appears to be the only biological function of some characterized NSAR/OSBS enzymes, while both activities are biologically relevant in others. The promiscuity model predicts that these enzymes evolved from an ancestral OSBS which promiscuously catalyzed NSAR as a side reaction that was not biologically relevant. If so, the model predicts that some extant OSBS enzymes would have low levels of promiscuous NSAR activity. This manuscript describes such an enzyme from Exiguobacterium sp. AT1b (ExiOSBS). We show that ExiOSBS efficiently catalyzes OSBS (kcat/KM=2.6×106M−1s−1), but its efficiency for the NSAR reaction is only 41M−1s−1. Moreover, genome context indicates that OSBS is the only biologically relevant activity. ExiOSBS diverged from the NSAR/OSBS subfamily before NSAR emerged as a biologically relevant activity. These results provide evidence that NSAR activity originated as a promiscuous activity in an ancestor of the NSAR/OSBS subfamily.
ISSN:0006-291X
1090-2104
DOI:10.1016/j.bbrc.2014.06.034