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Genome-wide screening reveals a novel class of carbonic anhydrase-like inorganic carbon transporters in chemoautotrophic bacteria

By John J. Desmarais, Avi I. Flamholz, Cecilia Blikstad, Eli J. Dugan, Thomas G. Laughlin, Luke M. Oltrogge, Allen W. Chen, Kelly Wetmore, Spencer Diamond, Joy Y Wang, David F. Savage

Posted 22 Nov 2018
bioRxiv DOI: 10.1101/476713

Many bacterial autotrophs rely on CO2 concentrating mechanisms (CCMs) to assimilate carbon. Although many CCM proteins have been identified, including a 200+ MDa protein organelle called the carboxysome, a systematic screen of CCM components has not been carried out. Here, we performed a genome-wide barcoded transposon screen to identify essential and CCM-related genes in the γ-proteobacterium H. neapolitanus. Our screen revealed an operon critical for CCM function which encodes a domain of unknown function (PFAM:PF10070) and putative cation transporter subunit (PFAM:PF00361). These two proteins, which we name DabA and DabB for "DABs accumulate bicarbonate," function as a heterodimeric, energy-coupled inorganic carbon pump in E. coli. Furthermore, DabA binds zinc and has a an active site homologous to a β-carbonic anhydrase. Based on these results, we propose that DABs function as vectorial CAs coupled to cation gradients and serve as inorganic carbon pumps throughout prokaryotic phyla.

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