Small Molecule Stabilization of Diverse Amyloidogenic Immunoglobulin Light Chains Revealed by Hydrogen-Deuterium Exchange Mass Spectrometry.

Immunoglobulin light chains, a component of antibodies, can misfold and aggregate to cause systemic AL amyloidosis. Aggregation, including amyloid fibril formation, requires unfolding of the full-length light chain from its native state, and in most cases aberrant proteolysis. Small molecules that bind to the native state of light chains to stabilize them against conformational excursions and proteolysis are under development as drug candidates for AL amyloidosis. Since each patient has a unique light chain sequence, a challenge for candidate stabilizer drugs is to bind multiple light chains and suppress their dynamics. Here, we used hydrogen-deuterium exchange coupled to mass spectrometry to characterize the binding of small molecule stabilizers to λ light chain proteins. We measured the effects of six small molecules on a previously studied light chain, then characterized a further six amyloidogenic light chains in the presence and absence of the most efficacious stabilizer. Despite structural and dynamic differences among the light chains, stabilizer binding led to decreased hydrogen exchange rates, consistent with reduced local and global unfolding. Protection upon binding was most prominent in residues within complementarity determining region 3 and framework region 4 of the light chain variable domains, which undergo major conformational changes enabling amyloid formation. Stabilizer binding reduced the rate at which all light chains were cleaved by protease, and delayed amyloid formation in vitro. These data show that these stabilizers suppress the range of conformational dynamics associated with light chain aggregation, supporting their therapeutic potential.