A Simulated Intermediate State for Folding and Aggregation Provides Insights into Delta N6 beta(2)-Microglobulin Amyloidogenic Behavior

A major component of ex vivo amyloid plaques of patients with dialysis-related amyloidosis (DRA) is a cleaved variant of beta(2)-microglobulin (Delta N6) lacking the first six N-terminal residues. Here we perform a computational study on Delta N6, which provides clues to understand the amyloidogenicity of the full-length beta(2)-microglobulin. Contrary to the wild-type form, Delta N6 is able to efficiently nucleate fibrillogenesis in vitro at physiological pH. This behavior is enhanced by a mild acidification of the medium such as that occurring in the synovial fluid of DRA patients. Results reported in this work, based on molecular simulations, indicate that deletion of the N-terminal hexapeptide triggers the formation of an intermediate state for folding and aggregation with an unstructured strand A and a native-like core. Strand A plays a pivotal role in aggregation by acting as a sticky hook in dimer assembly. This study further predicts that the detachment of strand A from the core is maximized at pH 6.2 resulting into higher aggregation efficiency. The structural mapping of the dimerization interface suggests that Tyr10, His13, Phe30 and His84 are hot-spot residues in Delta N6 amyloidogenesis.