Influence of the germline sequence on the thermodynamic stability and fibrillogenicity of human lambda 6 light chains

Light chain-associated amyloidosis is a fatal disease characterized by the aggregation and pathologic deposition of monoclonal light chain-related fragments as amyloid fibrils in organs or tissues throughout the body. Notably, it has been observed that proteins encoded by the lambda variable light chain (V-L) gene segment 6a are invariably associated with amyloid deposition; however, the contribution of the gene to this phenomenon has not been established. In this regard, we have determined the thermodynamic stability and kinetics of in vitro fibrillogenesis of a recombinant (r) V-L protein, designated 6aJL2, which contains the predicted sequences encoded by the 6a and JL2 germline genes. Additionally, studied a 6a mutant (6aJL2-Arg25Gly), that is present in similar to 25% of all amyloid-associated lambda 6 light chains. Remarkably, the wild-type 6aJL2 protein was more stable than were all known amyloidogenic kappa and lambda light chains for which stability parameters are available; more importantly, it was even more so (and less fibrillogenic) than the only clinically proven nonamyloidogenic lambda 6 protein, Jto. Conversely, the mutated 6aJL2-R25G molecule was considerably less stable and more fibrillogenic than was the native 6aJL2. Our data indicate that the propensity of lambda 6 light chains to form amyloid can not be attributed to thermodynamic instability of the germline-encoded V lambda 6 domain, but rather, is dependent on sequence alterations that render such proteins amyloidogenic.