| A tissue specific homologue of XIAP , known as ILP 2 ( IAP like protein 2 ) , has previously been implicated in the control of apoptosis in the testis by direct inhibition of caspase 9 . ^^^ Fusion of a 9 residue linker from XIAP to the N terminus of ILP 2 restored tight caspase 9 inhibition , dramatically increased conformational stability and allowed crystallization of the ILP 2 BIR domain in a form strikingly similar to the XIAP third BIR domain . ^^^ We conclude that ILP 2 is an unstable protein , and can not inhibit caspase 9 in a physiological way on its own . ^^^ |