The substrate tunnel of Nce103. A) The superposition between the active sites of Nce103 and P. sativum β-CA (subunit A). Nce103 is shown in green and P. sativum β-CA in magenta. Zinc ions in Nce103 and P. sativum β-CA are colored in gray and orange, respectively. The water molecule Wat263 is colored in red. Residues and the acetate in P. sativum β-CA are marked with prime. B) The line graphs of the tunnel profile. The X-coordinate shows the path step; and the Y-coordinate shows the tunnel radius. C) The simulated tunnel of Nce103. Subunit A and B are colored in cyan and red, respectively. The tunnel is colored in green. The missing loop region is labeled as a dashed line. D) A closer look at the tunnel.