Fig. 1: Cryo-EM structure of the human Stomatin complex reveals a 16-subunit cage with alternating conformers.

a Cryo-EM micrograph of native membrane vesicles containing N-terminal ALFA-tagged human Stomatin. Arrows indicate particles showing top and side views of the cap-like complex. This experiment was independently repeated three times with similar results. b Selected 2D class averages reveal top and side orientations, showing that the Stomatin complex forms a closed, symmetric ring partially embedded in the membrane. c 3D reconstruction of the 16-mer Stomatin oligomer, displaying alternating subunit conformations (Conformer A: blue; Conformer B: yellow). Shown are bottom (left) and side (right) views, with the complex anchored to the membrane via its wide end and the narrow end forming a central opening. d Structural dimensions and subunit arrangement of the complex. Bottom view (left) shows the alternating A/B pattern with numbered subunits. Side view (right) indicates the overall height (~10.4 nm), external width (~15.6 nm), internal diameter (~11.8 nm), and pore diameter at the narrow end (~1.8 nm). e Domain architecture of Stomatin conformers. Both share the same topology: Flexible N-terminus (pink), two short hydrophobic helices (H1 (purple) and H2 (blue)), SPFH1 and SPFH2 domains (cyan and green), followed by a short wall helix (WallH, yellow), a cap helix (CapH, orange), and a C-terminal β-barrel (orange red). Conformer A ends in a short helix, while Conformer B adopts a looped C-terminal region (red). f Structures of Conformer A and B. Side (left) and bottom (right) views highlight the domain organization and asymmetry in the ring. Insets show the conformers within the full oligomeric cage (bottom center) and a top-down view from the narrow end, where the β-barrel forms a central pore.