EMC chaperone activity is required for cotranslational calcium channel assembly.

EMC’s chaperone activity is required for cotranslational assembly of heterotrimeric voltage-gated calcium channels, with loss linked to premature degradation of nascent channels.

• Why it matters: Many human membrane proteins must form stoichiometric complexes during ER biogenesis, but how ER factors coordinate insertion, folding, and assembly is unclear.
• What they did: Using function-separating EMC mutations and inhibitory nanobodies, the study tested whether perturbing EMC’s chaperone function affects nascent CaV channel stability and engagement during cotranslational biogenesis.
• The result: Impairing EMC’s chaperone function caused premature degradation of nascent CaV channels and reduced CaV-dependent cardiomyocyte contraction; EMC engaged CaVα cotranslationally, requiring its first transmembrane domain bundle to protrude from the ribosome–translocon complex.

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