Localization of a conformational anomaly to the Fabmu region of a monoclonal IgM cryoglobulin.

The hydrodynamic (gel filtration and sedimentation) properties of an isolated monoclonal IgM-K cryoglobulin (McE.) and five non-cryoglobulin cold-soluble proteins, as well as their constituent monomeric subunits and (Fc)5mu and Fabmu fragments, are compared under both native and partially denaturing conditions. It is concluded that the cryoimmunoglobulin exhibits a significantly greater Stokes radius than the non-cryoglobulin reference proteins, and that this difference arises in the Fabmu region of the McE. molecule. When the proteins and their fragments are analysed by circular dichroism in the far u.v. region, an atypical conformation is again detected in the Fabmu region of the cryoglobulin. These findings are the first demonstration and partial structural localization of a conformation anomaly in a monoclonal cryoimmunoglobulin.