subhash bihani - X-ray structure reveals a new class and provides insight into evolution of alkaline phosphatase

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      Publication Details (including relevant citation   information):

      PLoS   ONE 6, 7: e22767 (2011).

      Abstract:

      The alkaline phosphatase (AP) is a bi-metalloenzyme of potential   applications in biotechnology and bioremediation, in

      which phosphate monoesters are nonspecifically hydrolysed under   alkaline conditions to yield inorganic phosphate. The

      hydrolysis occurs through an enzyme intermediate in which the   catalytic residue is phosphorylated. The reaction, which also

      requires a third metal ion, is proposed to proceed through a   mechanism of in-line displacement involving a trigonal

      bipyramidal transition state. Stabilizing the transition state by   bidentate hydrogen bonding has been suggested to be the

      reason for conservation of an arginine residue in the active   site. We report here the first crystal structure of alkaline

      phosphatase purified from the bacterium Sphingomonas. sp. Strain   BSAR-1 (SPAP). The crystal structure reveals many

      differences from other APs: 1) the catalytic residue is a   threonine instead of serine, 2) there is no third metal ion   binding

      pocket, and 3) the arginine residue forming bidentate hydrogen   bonding is deleted in SPAP. A lysine and an aspargine

      residue, recruited together for the first time into the active   site, bind the substrate phosphoryl group in a manner not

      observed before in any other AP. These and other structural   features suggest that SPAP represents a new class of APs.

      Because of its direct contact with the substrate phosphoryl   group, the lysine residue is proposed to play a significant role   in

      catalysis. The structure is consistent with a mechanism of   in-line displacement via a trigonal bipyramidal transition state.   The

      structure provides important insights into evolutionary   relationships between members of AP superfamily.

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