The residues 4 to 6 at the N-terminus in particular modulate fibril propagation of β2-microglobulin

The Delta N6 truncation is the main posttranslational modification of beta(2)-microglobulin (beta M-2) found in dialysis-related amyloid. Investigation of the interaction of wild-type (WT) beta M-2 with N-terminally truncated variants is therefore of medical relevance. However, it is unclear which residues among the six residues at the N-terminus are crucial to the interactions and the modulation of amyloid fibril propagation of beta M-2. We herein analyzed homo- and heterotypic seeding of amyloid fibrils of WT human beta M-2 and its N-terminally-truncated variants Delta N1 to Delta N6, lacking up to six residues at the N-terminus. At acidic pH 2.5, we produced amyloid fibrils in vitro from recombinant, WT beta M-2 and its six truncated variants, and found that Delta N6 beta M-2 fibrils exhibit a significantly lower conformational stability than WT beta M-2 fibrils. Importantly, under more physiological conditions (pH 6.2), we assembled amyloid fibrils in vitro only from recombinant, Delta N4, Delta N5, and Delta N6 beta M-2 but not from WT beta M-2 and its three truncated variants Delta N1 to Delta N3. Notably, the removal of the six, five or four residues at the N-terminus leads to enhanced fibril formation, and homoand heterotypic seeding of Delta N6 fibrils strongly promotes amyloid fibril formation of WT beta M-2 and its six truncated variants, including at more physiological pH 6.2. Collectively, these results demonstrated that the residues 4 to 6 at the N-terminus particularly modulate amyloid fibril propagation of beta M-2 and the interactions of WT beta M-2 with N-terminally truncated variants, potentially indicating the direct relevance to the involvement of the protein's aggregation in dialysis-related amyloidosis.