Journal: Cell Rep / Year: 2025 Title: Three cryo-EM structures of CD109 reveal its mechanism of protease inhibition. Authors: Ana V Almeida / Kathrine T Jensen / Seandean L Harwood / Martin H Jørgensen / Nadia S Nielsen / Ida B Thøgersen / Jan J Enghild / Gregers R Andersen / Abstract: CD109 is a glycosylphosphatidylinositol-anchored protein. In addition to regulating transforming growth factor β (TGF-β) network signaling, CD109 is also a protease inhibitor. Protease cleavage of ...CD109 is a glycosylphosphatidylinositol-anchored protein. In addition to regulating transforming growth factor β (TGF-β) network signaling, CD109 is also a protease inhibitor. Protease cleavage of its bait region triggers a conformational change releasing the major fragment from the cell surface, exposing a reactive thioester that can conjugate proteases. To understand this protease inhibition mechanism, we determined cryoelectron microscopy structures of CD109 in native, protease-activated, and methylamine-activated conformations. Despite CD109's low sequence similarity with the protease inhibitor A2ML1, CD109 adopts a similar protease-activated conformation, suggesting a shared mechanism of protease inhibition. Deglycosylation of CD109 does not affect chymotrypsin conjugation but enhances substrate access, suggesting that CD109 glycans contribute to protease inhibition. Our data provide a structural basis for understanding CD109's protease-triggered membrane release, its protease inhibitory mechanism, and additional biological functions.
Model: Au-flat 1.2/1.3 / Material: GOLD / Mesh: 300 / Support film - Material: GOLD / Support film - topology: CONTINUOUS / Support film - Film thickness: 1200 / Pretreatment - Type: GLOW DISCHARGE / Pretreatment - Time: 45 sec. / Pretreatment - Atmosphere: AIR
Vitrification
Cryogen name: ETHANE / Chamber humidity: 95 % / Chamber temperature: 279.15 K / Instrument: LEICA EM GP
Details
Monodisperse sample
-
Electron microscopy
Microscope
FEI TITAN KRIOS
Image recording
Film or detector model: GATAN K3 BIOQUANTUM (6k x 4k) / Number grids imaged: 2 / Number real images: 9975 / Average electron dose: 59.9 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
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