New insight into the catalytic mechanism of histidine phosphatases revealed by a functionally essential arginine within the active sites of the Sts phosphatases.

Sts-1 and Sts-2 are histidine phosphatases that negatively regulate TCR signaling pathways, including those involved in cytokine production. Histidine phosphatases (HPs) play key roles in such varied biological processes as metabolism, development, and intracellular signaling. They differ considerably in primary sequence and substrate specificity, but possess a catalytic core formed by an invariant quartet of active site residues. Two histidines and two arginines cluster together within the HP active site and are thought to participate in a two-step dephosphorylation reaction. To date there has been little insight into additional residues that might play an important functional role. Herein, we identify and characterize an additional residue within the Sts phosphatases (Sts-1 Arg-383 or Sts-2 Arg-369) that is critical for catalytic activity and intracellular function. Mutation of Sts-1 Arg-383 to alanine compromises enzyme activity and renders Sts-1 unable to suppress TCR-induced cytokine induction. Of multiple amino acids substituted for Arg-383, only lysine partially rescues Sts-1 catalytic activity. Although Sts-1 Arg-383 is conserved in all Sts homologues, it is only conserved in one of the two sub-branches of HPs. These results highlight an essential role for Sts-1 phosphatase activity in regulating T cell activation and add a new dimension of complexity to our understanding of HP catalytic activity.

Source: BJ Signal - April 9, 2013 Category: Biochemistry Authors: B San Luis, N Nassar, N Carpino Tags: BJ Signal Source Type: research