MST1 contains multiple disulfide bonds organized in a spiral-like way. (A) MST1 protein contains multiple disulfide bonds arranged in a spiral-like configuration. Disulfide bonds are distributed across the SD and Ig5-9 domains. Notably, the SD tandem of MST1 exhibits a remarkable array of disulfide bonds, regularly spaced at ∼11-Å intervals, except for SDc (1,480–1,545 AA), where the spacing is about 19.6 Å, and SDd (1,628–1,665 AA), with a spacing of ∼19 Å. (B) Visualization of disulfide bonds in mastigoneme filament. Colored dots represent the disulfide bonds, forming a long ladder-like structure within the filament. The left panel presents a horizontal view, while the right panel, turned 90°, offers a top view. (C) Cryo-EM image of mastigoneme filaments prepared with 0, 1, 5, and 20 mM DTT (bar = 10 nm). (D and E) Statistical analysis of the number (D) and the frequency (E) of mastigoneme numbers appearing in each image. The measurements related to the percentage and distribution of mastigoneme in cryo-EM images.
