In a cell free system , binding of a protein fragment ( 1340 1579 ) containing a pdz domain 2 3 from __NODE__ protein and a protein fragment ( aa sequence IQSLV ) from __NODE__ protein is greater than binding of a protein fragment ( 1340 1579 ) containing a pdz domain 2 3 from __NODE__ protein and a protein fragment ( aa sequence QSLV ) from __NODE__ protein .