Fig. 3: Close-up view of the intramolecular interface between the N- and C-terminal regions of SOD1 fibril.

a The primary sequence of the SOD1 fibril core. The cyan bar marks the N-terminal half of the interface and the blue bar marks the C-terminal half. The dotted lines correspond to residues 56 to 85 not modeled in the cryo-EM density and represent an internal disordered segment between the N- and C-terminal regions of SOD1 fibril. b A space-filled model overlaid onto stick representation of the SOD1 fibril, in which the N-terminal segment is shown in cyan and the C-terminal segment in blue. Lys/Asp pairs, His/Asp pairs, and His/Glu pairs that form salt bridges are highlighted in red (oxygen atoms in Asp and Glu) and blue (nitrogen atom in Lys and His), and the intramolecular interface is magnified in c to e. c–e Magnified top views of the three regions of the intramolecular L-shaped interface between the N- and C-terminal regions of SOD1 fibril, where three pairs of amino acids (Lys36 and Asp109; His43 and Asp101; and His46 and Glu100) form three salt bridges. Two side views (right) highlighting a strong salt bridge between Glu100 from the C-terminal segment (i) and His46 from the adjacent N-terminal segment (i + 1), with a distance of 2.2 Å (red), or between Asp101 from the molecular layer (i–1) of the C-terminal region and His43 from the molecular layer (i + 2) of the N-terminal region, with a distance of 2.8 Å (red). A side view (right) highlighting a strong salt bridge between Asp109 from the C-terminal part (i) and Lys36 from the adjacent N-terminal part (i + 1), with a distance of 3.0 Å (red).