3-DIMENSIONAL ARCHITECTURE OF HUMAN ALPHA-2-MACROGLOBULIN TRANSFORMED WITH METHYLAMINE

A frozen-hydrated sample embedded in vitreous ice of human α2-macroglobulin transformed by methylamine was imaged by cryoelectron microscopy and reconstructed in three dimensions. In the reconstruction, the cage-like architecture of this protease inhibitor is fully revealed with a clear visualization of two lozenge-shaped lateral walls connected by thin bridges. The shape and dimensions of the internal cavity normally containing the trapped protease(s) is described. The possible locations of the thiol ester sites and intersubunit connections are also discussed.