Structure of V143I CA II. (a) Overall structure of V143I-0atm: V143I CA II with no CO2 pressurization. The active site (red box) is located at a depth of 15 Å from the surface. Note that Ile143 is located at the hydrophobic pocket in the active site. (b) Ordered water network in the hydrophilic region serving as a proton-transfer pathway. (c) Surface rendition of V143I-0atm. The entrance conduit (diameter of 7–10 Å, guided with a yellow dotted line) connects the active site to the bulk solvent outside, forming the replenishment pathway. The electron density of the entrance-conduit waters is contoured at 1.5σ. Hydrophobic amino acids are shaded in red, while hydrophilic amino acids are coloured white.