Crystals of the human heavy chain disease protein Riv and human Fc fragment are isomorphous: further evidence for conformational flexibility in the hinge region of immunoglobulins.

Protein Riv is a human gamma 1 heavy chain disease immunoglobulin variant with a deletion of the entire VH and CH1 domains and consisting of most of the hinge region plus the CH2 and CH3 domains. Crystals of this protein are orthorhombic, belonging to the space group P2(1)2(1)2(1), with a = 80.1 A, b = 145.5 A, c = 50.1 A. These crystals are shown to be isomorphous with crystals of a human Fc fragment, indicating that the hinge region and the initial part of the CH2 domain of protein Riv do not assume a unique conformation in the crystalline state.