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  • Title: The structure of Neurospora crassa 3-carboxy-cis,cis-muconate lactonizing enzyme, a beta propeller cycloisomerase.
    Author: Kajander T, Merckel MC, Thompson A, Deacon AM, Mazur P, Kozarich JW, Goldman A.
    Journal: Structure; 2002 Apr; 10(4):483-92. PubMed ID: 11937053.
    Abstract:
    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 MLE, Neurospora crassa 3-carboxy-cis,cis-muconate lactonizing enzyme (NcCMLE) at 2.5 A 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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