Alpha-2-macroglobulins (A2Ms) are plasma proteins that trap and inhibit a broad range of proteases and are major components of the eukaryotic innate immune system. However, A2M-like proteins were identified in pathogenically invasive bacteria and species that colonize higher eukaryotes. This domain is found in eukaryotic and bacterial proteins. In human A2Ms, this domain encompasses macroglobulin-like domain MG5 and 6 including bait region. In Salmonella enterica ser A2Ms, this domain encompasses MG7 and MG8 including the bait region [1] [2]. The Bait region is cleaved by proteases, followed by a large conformational change that blocks the target protease within a cage-like complex. This model of protease entrapment is recognised as the Venus flytrap mechanism [1].

1: Structure of a bacterial alpha2-macroglobulin reveals mimicry of eukaryotic innate immunity. Wong SG, Dessen A; Nat Commun. 2014;5:4917. PMID:25221932

2: The crystal structure of human alpha2-macroglobulin reveals a unique molecular cage. Marrero A, Duquerroy S, Trapani S, Goulas T, Guevara T, Andersen GR, Navaza J, Sottrup-Jensen L, Gomis-Ruth FX; Angew Chem Int Ed Engl. 2012;51:3340-3344. PMID:22290936