Binding of heterodimer consisting of protein fragment ( 203 467 ) containing a ligand binding domain from mutant __SP__ __NODE__ protein ( with its AF 2 domain mutated ) and of protein fragment containing a ligand binding domain from mutant OR 1 [__NODE__] protein ( with its AF 2 domain mutated ) and a protein fragment ( 431 1158 ) from __SP__ __NODE__ protein occurs in cell free system .