3.B.1.1.7
Na⁺-pumping glutaconyl-CoA decarboxylase, Gcd, with subunits A₄/B₂/C1₁/C2₁/D₂ (The stoichiometry of the subunits is given by the subscripts.). Gcd drives the endergonic translocation of Na⁺ across the membrane with the exergonic decarboxylation of glutaconyl-CoA (ΔG⁰’ ≈−30 kJ/mol) to crotonyl-CoA. Vitt et al. 2020 reported on the molecular characterization of Gcd from Clostridium symbiosum. The subunit composition is four GcdA (65 kDa), two GcdB (35 kDa), one GcdC1 (15 kDa), one GcdC2 (14 kDa), and two GcdD (10 kDa). Low-resolution structural information was achieved by electron microscopic (EM) measurements, which resulted in a 3D reconstruction model based on negative-stained particles. The Gcd structure is built up of a membrane-spanning base primarily composed of the GcdB dimer and a solvent-exposed head with the GcdA tetramer as the major component. These two globular parts are bridged by a linker presumably built up of segments of GcdC1, GcdC2 and the 2 GcdDs. The structure of the highly mobile Gcd complex represents a template for the global architecture of the Bdc family (Vitt et al. 2020).