In __SP__ , binding of ligand binding domain from __SP__ __NODE__ protein and a protein fragment ( 421 1263 ) containing a receptor binding domain from frog __NODE__ protein is greater than binding of ligand binding domain from __SP__ __NODE__ protein and a mutant protein fragment ( 421 1263 ) ( L?A with its LXXLL motif 3 mutated ) containing a receptor binding domain from frog __NODE__ protein .