The unique structure of carbonic anhydrase αCA1 from
Abstract:Chlamydomonas reinhardtiiα‐type carbonic anhydrase (Cr‐αCA1) is a dimeric enzyme that catalyses the interconversion of carbon dioxide and carbonic acid. The precursor form of Cr‐αCA1 undergoes post‐translational cleavage and N‐glycosylation. Comparison of the genomic sequences of precursor Cr‐αCA1 and other αCAs shows that Cr‐αCA1 contains a different N‐terminal sequence and two insertion sequences. A 35‐residue peptide in one of the insertion sequences is deleted from the precursor during maturation. The crystal structure of the mature form of Cr‐αCA1 has been determined at 1.88 Å resolution. Each subunit is cleaved into the long and short peptides, but they are linked together by a disulfide bond. The two subunits are linked by a disulfide bond. N‐Glycosylations occur at three asparagine residues and the attached N‐glycans protrude into solvent regions. The subunits consist of a core β‐sheet structure composed of nine β‐strands. At the centre of the β‐sheet is the catalytic site, which contains a Zn atom bound to three histidine residues. The amino‐acid residues around the Zn atom are highly conserved in other monomeric and dimeric αCAs. The short peptide runs near the active site and forms a hydrogen bond to the zinc‐coordinated residue in the long chain, suggesting an important role for the short peptide in Cr‐αCA1 activity.
Document Type: Research Article
Publication date: 2011-10-01