In __SP__ , binding of mutant __SP__ __NODE__ protein ( N terminal truncation 1 1453 ) and mutant __NODE__ protein ( N terminal truncation 1 136 with its hinge domain and its ligand binding domain retained ) is greater than binding of mutant __SP__ __NODE__ protein ( N terminal truncation 1 1453 ) and mutant __NODE__ protein ( N terminal truncation 1 165 with its hinge domain and its ligand binding domain retained ) .