In a cell free system , binding of mutant __SP__ __NODE__ protein ( C terminal truncation 135 End with its pleckstrin homology ( PH ) domain retained ) and __NODE__ 3 , diphosphate is greater than binding of mutant __SP__ __NODE__ protein ( C terminal truncation 135 End with its pleckstrin homology ( PH ) domain retained ) and __NODE__ 3 , trisphosphate .