Question

A signaling protein with both a SH2 and a SH3 domain binds to the phosphorylated form of its target protein with a Kd of 0.23 nM. The affinity of the SH3 domain by itself is 41 uM and the phosphotyrosine contact with the SH2 domain is responsible for 22 kJ/mol. What is the Kd of the SH2 domain for non-phosphorylated target?