Cloning, expression and mutational analysis of SH-PTP2, human protein-tyrosine phosphatase

A human cDNA clone encoding a nonreceptor protein-tyrosine-phosphatase (PTP) has been isolated and sequenced. The 2.1 kilobase pair cDNA encodes for a 593 amino acid protein that contains a single tyrosine phosphatase catalytic domain at the C-terminus. At the N-terminus the protein has two adjacent copies of Src homology region (SH2 domain) which show 61% and 73% identity at the amino acid level to the SH2 domains of the human PTP1C and Drosophila corkscrew protein, respectively. The overall homology between SH-PTP2 and PTP1C or to corkscrew protein is 58%. When this protein (or its catalytic domain) was expressed in E. coli as a glutathione-S-transferase fusion protein tyrosine-phosphatase activity was detected in bacterial cell extracts. Site-directed mutation made at the conserved cysteine (459) residue to serine within the highly conserved VHCXAGXXR sequence in the PTP catalytic domain resulted in complete loss of enzymatic activity demonstrating the importance of this cysteine residue in catalysis. Northern blot analysis showed that SH-PTP2 is expressed as a 6.5 kilobase mRNA in a number of fetal and adult human tissues and cell lines. The highest levels of its mRNA were detected in fetal brain and in adult heart tissue. The identification of SH-PTP2 along with PTP1C and corkscrew protein suggest that there exist a family of nonreceptor PTP containing SH2-domain which will participate in specific signal transduction pathways involving tyrosine phosphorylation-dephosphorylation.