Domain Motions in Protein Crystals
Protein domains and elements of secondary structure such as α-helices form pseudo-rigid bodies which can move as a result of environmental forces. The binding of inhibitor molecules to enzyme molecules can result in relative movement of domains and crystal packing forces may also cause conformational changes in proteins which may result in loss of activity in the case of enzymes. The first study reported here analyses the conformational changes which take place in a range of closely related crystal structures and compares them to the rigid body domain motion in one of the structures determined form X-ray analysis of rigid body thermal parameters. The second study reports the structure of an eye lens protein which is homologous to the enzyme argininosuccinate lyase which crystallises in low and high pH forms. The high pH form exhibits a structure consisting of hexagonal close packing of supramolecular helices. The domain motions in these helices give rise to a remarkable diffuse X-ray diffraction pattern with 14-fold symmetry indicating that these supramolecular helices may be stable entities outside the crystal.
KeywordsRigid Body Protein Crystal Aspartic Proteinase Hexagonal Close Packing Screw Axis
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