Novel protein tyrosine phosphatase substrate-trapping double mutant and uses thereof

A method for identifying a substrate of a protein tyrosine phosphatase (PTP) enzyme, comprising the steps of:

• (a) contacting a candidate substrate with at least one PTP enzyme in which the invariant aspartate residue and the invariant glutamine residue are each replaced with a replacement amino acid residue, wherein the replacement residues together cause a reduction in catalytic rate (kcat) of the enzyme and an increase in substrate-binding affinity (Kd) of the enzyme;
• and
• (b) assessing the ability of the candidate agent to bind to the PTP enzyme.

A kit for identifying a substrate of a protein tyrosine phosphatase (PTP) enzyme, comprising:

• (a) at least one PTP enzyme in which the invariant aspartate residue and the invariant glutamine residue are each replaced with a replacement amino acid residue, wherein the replacement residues together cause a reduction in catalytic rate (kcat) of the enzyme and an increase in substrate-binding affinity (Kd) of the enzyme;
• and
• (b) reagents suitable for detecting binding of the PTP enzyme to a candidate substrate.