The co-crystal structure of Bn86287 (cf. Figure ) and all2909 (cf. Figure ) with HCO3 - demonstrate the overall architecture of the metal-free CA. Interestingly, similar to other metal-containing CA (cf. Figure ), the metal-free CA also displays a 'bipolar' nature (cf. Figure ), with distinct hydrophilic and hydrophobic zones. As shown in Figure , HCO3 -is found in the hydrophilic, bent, finger-like cavity of the enzyme. In contrast, CO2 is hydrophobic, which significantly reduces the likelihood of it being found in the same location as HCO3 -. Instead, CO2 tends to bind with the hydrophobic region of the metal-free Bn86287.