Publication Details (including relevant citation information):
PLoS ONE 6, 7: e22767 (2011).
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.
Address (URL): http://