J Michael Sauder - Evolution of enzymatic activities in the enolase superfamily: stereochemically distinct mechanisms in two families of cis,cis-muconate lactonizing enzymes

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      Publication Details (including relevant citation   information):

      Biochemistry (2009) 48: 1445-1453.

      Sakai A, Fedorov AA, Fedorov EV, Schnoes AM, Glasner ME, Brown S,   Rutter ME, Bain K, Chang S, Gheyi T, Sauder JM, Burley SK,   Babbitt PC, Almo SC, Gerlt JA

      Abstract:

      The mechanistically diverse enolase superfamily is a paradigm   for  elucidating Nature's strategies for divergent evolution   of enzyme  function. Each of the different reactions   catalyzed by members of the  superfamily is initiated by   abstraction of the alpha-proton of a  carboxylate substrate   that is coordinated to an essential Mg(2+). The  muconate   lactonizing enzyme (MLE) from Pseudomonas putida, a member of   a  family that catalyzes the syn-cycloisomerization of   cis,cis-muconate to  (4S)-muconolactone in the   beta-ketoadipate pathway, has provided  critical insights   into the structural bases for evolution of function  within   the superfamily. A second, divergent family of homologous   MLEs  that catalyzes anti-cycloisomerization has been   identified. Structures  of members of both families liganded   with the common (4S)-muconolactone  product (syn,   Pseudomonas fluorescens, gi 70731221; anti, Mycobacterium    smegmatis, gi 118470554 ) document that the conserved Lys at the   end of  the second beta-strand in the   (beta/alpha)(7)beta-barrel domain serves  as the acid   catalyst in both reactions. The different stereochemical    courses (syn and anti) result from different structural   strategies for  determining substrate specificity: although   the distal carboxylate group  of the cis,cis-muconate   substrate attacks the same face of the proximal  double   bond, opposite faces of the resulting enolate anion   intermediate  are presented to the conserved Lys acid   catalyst. The discovery of two  families of homologous, but   stereochemically distinct, MLEs likely  provides an example   of "pseudoconvergent" evolution of the same function  from   different homologous progenitors within the enolase   superfamily,  in which different spatial arrangements of   active site functional groups  and substrate specificity   determinants support catalysis of the same  reaction.

      Address (URL): http://pubs.acs.org/doi/abs/10.1021/bi802277h