Thermodynamic modulation of light chain amyloid fibril formation

To obtain further insight into the pathogenesis of amyloidosis and develop therapeutic strategies to inhibit fibril formation we investigated: 1) the relationship between intrinsic physical properties (thermodynamic stability and hydrogen-deuterium (H-D) exchange rates) and the propensity of human i mmunoglobulin light chains to form amyloid fibrils in vitro; and 2) the eff ects of extrinsically modulating these properties on fibril formation. An a myloid-associated protein readily formed amyloid fibrils in vitro and had a lower free energy of unfolding than a homologous nonpathological protein, which did not form fibrils in vitro. H-D exchange was much faster for the p athological protein, suggesting it had a greater fraction of partially fold ed molecules. The thermodynamic stabilizer sucrose completely inhibited fib ril formation by the pathological protein and shifted the values for its ph ysical parameters to those measured for the nonpathological protein in buff er alone. Conversely, urea sufficiently destabilized the nonpathological pr otein such that its measured physical properties were equivalent to those o f the pathological protein in buffer, and it formed fibrils. Thus, fibril f ormation by light chains is predominantly controlled by thermodynamic stabi lity; and a rational strategy to inhibit amyloidosis is to design high affi nity ligands that specifically increase the stability of the native protein .