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Structural Basis of Membrane Potential Coupled Vectorial CO₂ Hydration by the DAB2 Complex in Chemolithoautotrophs

ABSTRACT: The fixation of dissolved inorganic carbon (DIC) such as CO2 and bicarbonate is fundamental to the global primary production. Many autotrophs depend on a diversity of CO2-concentrating mechanisms (CCMs) to overcome the inefficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase and the limited supply of DIC. While cyanobacterial CCMs are well characterized, analogous systems in chemolithoautotrophs, specifically active DIC uptake systems have long been overlooked. Here, we present the first cryo-EM analysis of DAB2, an essential membrane-associated complex for CO₂ uptake in Halothiobacillus neapolitanus. The cytoplasmic subunit DabA2 displays a β-carbonic anhydrase-like fold, while the transmembrane subunit DabB2 resembles the proton-conducting subunits of respiratory Complex I. Purified DAB2 binds CO₂ independent of proton motive force (PMF) however, did not spontaneously hydrate CO2. Structural analysis reveals a deeply buried active site only accessible via gated substrate tunnels, suggesting substrate access and catalysis are tightly regulated. The transmembrane helix of DabA2 forms the proton pathway and potentially couples proton translocation to the catalysis. These features define a vectorial CO2 hydration mechanism that prohibits reverse bicarbonate dehydration. Our findings establish DAB2 as a prototype of a previously unrecognized family of PMF-driven carbonic anhydrases, elucidating a novel strategy for CO₂ capture in non-photosynthetic autotrophs.

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ORGANISM(S): Escherichia Coli

SUBMITTER: Timo Glatter

LAB HEAD: Timo Glatter

PROVIDER: PXD076189 | Pride | 2026-04-17

REPOSITORIES: Pride

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