Mtcb, A Member Of The Mttb Superfamily From The Human Gut Acetogen Eubacterium Limosum, Is A Cobalamin-Dependent Carnitine Demethylase

The RhopH complex is implicated in malaria parasites’ ability to invade and create new permeability pathways in host erythrocytes, but its mechanisms remain poorly understood. Here we enrich the endogenous RhopH complex in a native soluble form, comprising RhopH2, CLAG3.1 and RhopH3, directly from parasite cell lysates and determine its atomic structure using cryo electron microscopy, mass spectrometry, and the cryoID program. This first direct observation of an exported P. falciparum transmembrane protein—in a soluble, trafficking state and with atomic details of buried putative membrane-insertion helices—offers insights into assembly and trafficking of RhopH and other parasite-derived complexes to the erythrocyte membrane. Our study demonstrates the potential endogenous structural proteomics approach holds for elucidating the molecular mechanisms of hard-to-isolate complexes in their native, functional forms.