Journal
STRUCTURE
Volume 10, Issue 4, Pages 483-492Publisher
CELL PRESS
DOI: 10.1016/S0969-2126(02)00744-X
Keywords
addition-elimination reaction; beta propeller convergent evolution; muconate lactonizing enzyme; X-ray structure
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Muconate lactonizing enzymes (MLEs) convert cis,cis-muconates to muconolactones in microbes as part of the beta-ketoadipate pathway; some also dehalogenate muconate derivatives of xenobiotic haloaromatics. There are three different MLE classes unrelated by evolution. We present the X-ray structure of a eukaryotic MILE, Neurospora crassa 3-carboxy-cis,cis-muconate lactonizing enzyme (NcCMLE) at 2.5 Angstrom resolution, with a seven-bladed beta propeller fold. It is related neither to bacterial MLEs nor to other beta propeller enzymes, but is structurally similar to the G protein beta subunit. It reveals a novel metal-independent, cycloisomerase motif unlike the bacterial metal cofactor MLEs. Together, the bacterial MLEs and NcCMLE structures comprise a striking structural example of functional convergence in enzymes for 1,2-addition-elimination of carboxylic acids. NcCMLE and bacterial MLEs may enhance the reaction rate differently: the former by electrophilic catalysis and the latter by electrostatic stabilization of the enolate.
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