In __SP__ , binding of mutant __SP__ __NODE__ protein ( N terminal truncation 1 279 with its ligand binding domain retained ) and __SP__ __NODE__ protein is greater than binding of mutant __SP__ __NODE__ protein ( N terminal truncation 1 279 with its ligand binding domain retained ) and mutant __SP__ __NODE__ protein ( L147A L148A with its __NODE__ zipper domain 2 mutated ) .