How calcium inhibits the magnesium-dependent enzyme human phosphoserine phosphatase.
The structure of the Mg(2+)-dependent enzyme human phosphoserine phosphatase (HPSP) was exploited to examine the structural and functional role of the divalent cation in the active site of phosphatases. Most interesting is the biochemical observation that a Ca(2+) ion inhibits the activity of HPSP, even in the presence of added Mg(2+). The sixfold coordinated Mg(2+) ion present in the active site of HPSP under normal physiological conditions, was replaced by a Ca(2+) ion by using a crystallization condition with high concentration of CaCl(2) (0.7 m). The resulting HPSP structure now shows a sevenfold coordinated Ca(2+) ion in the active site that might explain the inhibitory effect of Ca(2+) on the enzyme. Indeed, the Ca(2+) ion in the active site captures both side-chain oxygen atoms of the catalytic Asp20 as a ligand, while a Mg(2+) ion ligates only one oxygen atom of this Asp residue. The bidentate character of Asp20 towards Ca(2+) hampers the nucleophilic attack of one of the Asp20 side chain oxygen atoms on the phosphorus atom of the substrate phosphoserine.
Peeraer
Yves
Y
Laboratory for Analytical Chemistry and Medicinal Physicochemistry, Faculty of Pharmaceutical Sciences, K.U. Leuven, Leuven, Belgium.
Rabijns
Anja
A
Collet
Jean-François
JF
Van Schaftingen
Emile
E
De Ranter
Camiel
C
D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002413:Cations, Divalent / Q000378:metabolism / Q000494:pharmacology; D018360:Crystallography, X-Ray; D006801:Humans; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D010768:Phosphoserine / Q000378:metabolism; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
D002413:Cations, Divalent; D010768:Phosphoserine; D010744:Phosphoric Monoester Hydrolases; C022394:phosphoserine phosphatase; D008274:Magnesium; D002118:Calcium