Structural Investigations of Human A2M Identify a Hollow Native Conformation That Underlies Its Distinctive Protease-Trapping Mechanism

• DOI: 10.1016/j.mcpro.2021.100090
• Publication Date: 2021-05-06T15:45:14Z
• Authors: Seandean Lykke Ha...; Jeppe Lyngsø; Alessandra Zarant...; Katarzyna Kjøge; Peter Kresten Nie...; Gregers Rom Andersen; Jan Skov Pedersen; Jan J. Enghild
• Keywords: Tetramer; Conformational change; Cleavage (geology)

Human α2-macroglobulin (A2M) is the most characterized protease inhibitor in alpha-macroglobulin (αM) superfamily, but structure of its native conformation has not been determined. Here, we combined negative stain electron microscopy (EM), small-angle X-ray scattering (SAXS), and cross-linking-mass spectrometry (XL-MS) to investigate A2M collapsed conformations that are obtained through aminolysis thiol ester by methylamine or cleavage bait region trypsin. The interpretation these data resulted a model tetramer conformational changes. Native consists two crescent-shaped disulfide-bridged subunit dimers, which face toward each other surround central hollow space. In A2M, interactions across dimers minimal, with single major interface between linker (LNK) regions oppositely positioned subunits. Bait induces both intrasubunit domain repositioning an altered configuration dimer. These changes collapse into more compact conformation, encloses interior protease-trapping cavity. A recombinant modified was used map region's position XL-MS. second introduced intersubunit disulfide LNK region, demonstrating predicted A2M. Altogether, our provides structural foundation for understanding A2M's mechanism, conformation-dependent receptor interactions, dissociation due inflammatory oxidative stress.