Conformational change with peptide bound in hole “b.” Structures of rfD-BβD432A+GH (A) and rfD+BOTH (normal fibrinogen with both GPRP and GHRP; B) are shown. Residues involved in β2 calcium and peptide binding are shown as pink sticks. Note the conformational change in residues Bβ397Glu and Bβ398Asp when peptide (shown as blue sticks) is bound to hole “b,” as in the case of normal. In the rfD-BβD432A+GH structure, hole “b” does not bind the peptide so that Bβ398Asp, together with γ132Glu, coordinates the β2 calcium (shown as orange sphere) that tethers the βC-module to the coiled coil.