Human l‐3‐phosphoserine phosphatase: sequence, expression and evidence for a phosphoenzyme intermediate

Abstract

We report the sequence of the cDNA encoding human l‐3‐phosphoserine phosphatase. The encoded polypeptide contains 225 residues and shows 30% sequence identity with the Escherichia coli enzyme. The human protein was expressed in a bacterial expression system and purified. Similar to known l‐3‐phosphoserine phosphatases, it catalyzed the Mg²⁺‐dependent hydrolysis of l‐phosphoserine and an exchange reaction between l‐serine and l‐phosphoserine. In addition we found that the enzyme was phosphorylated upon incubation with l‐[³²P]phosphoserine, which indicates that the reaction mechanism proceeds via the formation of a phosphoryl‐enzyme intermediate. The sensitivity of the phosphoryl‐enzyme to alkali and to hydroxylamine suggests that an aspartyl‐ or a glutamyl‐phosphate was formed. The nucleotide sequence of the cDNA described in this article has been deposited in the EMBL data base under accession number Y10275.