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

Abstract

The ΔN6 truncation is the main posttranslational modification of β2-microglobulin (β2M) found in dialysis-related amyloid. Investigation of the interaction of wild-type (WT) β2M 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 β2M. We herein analyzed homo- and heterotypic seeding of amyloid fibrils of WT human β2M and its N-terminally-truncated variants ΔN1 to ΔN6, lacking up to six residues at the N-terminus. At acidic pH 2.5, we produced amyloid fibrils in vitro from recombinant, WT β2M and its six truncated variants, and found that ΔN6 β2M fibrils exhibit a significantly lower conformational stability than WT β2M fibrils. Importantly, under more physiological conditions (pH 6.2), we assembled amyloid fibrils in vitro only from recombinant, ΔN4, ΔN5, and ΔN6 β2M but not from WT β2M and its three truncated variants ΔN1 to ΔN3. Notably, the removal of the six, five or four residues at the N-terminus leads to enhanced fibril formation, and homo- and heterotypic seeding of ΔN6 fibrils strongly promotes amyloid fibril formation of WT β2M 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 β2M and the interactions of WT β2M with N-terminally truncated variants, potentially indicating the direct relevance to the involvement of the protein’s aggregation in dialysis-related amyloidosis.

Keywords

• human β₂-microglobulin
• amyloid fibril
• conformational stability
• truncated variant
• fibril propagation
• atomic force microscopy