Sequence alignment of human CAs I (RCSB accession code 1CAB; ref. 61),
II (1CA2; ref. 47), IV (1ZNC; ref. 35), and XII, mouse CAs IV (2ZNC;
ref. 54) and V (1DMY; ref. 58), and rat CA III (1FLJ; ref. 62) based on
the alignment of secondary structural elements as observed in the
individual crystal structures. Blue and green shading denote
β-strands and α-helices, respectively. Residues conserved
throughout all of these sequences are colored red and residues at the
CA XII dimer interface are underlined. Triangles (▴) mark
histidine–zinc ligands and asterisks (*) denote asparagine
glycosylation sites. The alignment is numbered according to the
sequence of human CA II. The entire sequence of CA XII is shown, and
the GXXXG and GXXXS motifs that signal transmembrane helix dimerization
are underlined in red; potential phosphorylation sites are double
underlined. For all other isozymes, the N and C termini are truncated
according to what is visible in each crystal structure.