Bacterial ι-CAs

Abstract

Recent research has identified a novel class of carbonic anhydrases (CAs), designated ι-CA, predominantly found in marine diatoms, eukaryotic algae, cyanobacteria, bacteria, and archaea genomes. This class has garnered attention owing to its unique biochemical properties and evolutionary significance. Through bioinformatic analyses, LCIP63, a protein initially annotated with an unknown function, was identified as a potential ι-CA in the marine diatom Thalassiosira pseudonana. Subsequent biochemical characterization revealed that LCIP63 has CA activity and its preference for manganese ions over zinc, indicative of evolutionary adaptation to marine environments. Further exploration of bacterial ι-CAs, exemplified by Burkholderia territorii ι-CA (BteCAι), demonstrated catalytic efficiency and sensitivity to sulfonamide and inorganic anion inhibitors, the classical CA inhibitors (CAIs). The classification of ι-CAs into two variant types based on their sequences, distinguished by the COG4875 and COG4337 domains, marks a significant advancement in our understanding of these enzymes. Structural analyses of COG4337 ι-CAs from eukaryotic microalgae and cyanobacteria thereafter revealed a distinctive structural arrangement and a novel catalytic mechanism involving specific residues facilitating CO₂ hydration in the absence of metal ion cofactors, deviating from canonical CA behavior. These findings underscore the biochemical diversity within the ι-CA class and highlight its potential as a target for novel antimicrobial agents. Overall, the elucidation of ι-CA properties and mechanisms advances our knowledge of carbon metabolism in diverse organisms and underscores the complexity of CA evolution and function.

Keywords: Carbonic anhydrases; Catalytic mechanism; Enzyme activity; Free metal CA; Iota-CA, bacteria.