Carbonic anhydrase is an ancient enzyme widespread in prokaryotes

Abstract

Carbonic anhydrases catalyze the reversible hydration of CO2 and are ubiquitous in highly evolved eukaryotes. The recent identification of a third class of carbonic anhydrase (␥ class) in a methanoarchaeon and our present finding that the ␤ class also extends into thermophilic species from the Archaea domain led us to initiate a systematic search for these enzymes in metabolically and phylogenetically diverse prokaryotes. Here we show that carbonic anhydrase is widespread in the Archaea and Bacteria domains, and is an ancient enzyme. The occurrence in chemolithoautotrophic species occupying deep branches of the universal phylogenetic tree suggests a role for this enzyme in the proposed autotrophic origin of life. The presence of the ␤ and ␥ classes in metabolically diverse species spanning the Archaea and Bacteria domains demonstrates that carbonic anhydrases have a far more extensive and fundamental role in prokaryotic biology than previously recognized. Carbonic anhydrase is a zinc-containing enzyme catalyzing the reversible hydration of CO 2 [CO 2 ϩ H 2 O º HCO 3 Ϫ ϩ H ϩ ]. Since the discovery of the enzyme in bovine erythrocytes in 1933 (1), isozymes have been found in virtually all mammalian tissues and cell types, where they function in CO 2 transport and other physiological processes (2). Carbonic anhydrases are also abundant in plants and unicellular green algae, where they are essential for photosynthetic CO 2 fixation (3). Although they are ubiquitous in highly evolved organisms from the Eukarya, the extent to which carbonic anhydrases occur in the Archaea and Bacteria domains is unknown; the enzyme has been purified from only five prokaryotic species (4-8) since 1963, when it was first identified in Neisseria sicca (9).All carbonic anhydrases are divided into three distinct classes (␣, ␤, and ␥) that evolved independently and have no sequence homology (10). Carbonic anhydrases from mammals (including the 10 active human isoforms) (10, 11), together with the two periplasmic enzymes from the unicellular green alga Chlamydomonas reinhardtii (12, 13), belong to the ␣ class. The ␤ class is comprised of enzymes from the chloroplasts of both monocotyledonous and dicotyledonous plants (10). Within the Bacteria domain, the enzymes purified from Neisseria gonorrhoeae and Escherichia coli also belong to the ␣ and ␤ classes (14, 15), respectively. Recently, a gene encoding a putative ␤ type carbonic anhydrase in the methanoarchaeon Methanobacterium thermoautotrophicum was expressed in E. coli and found to encode a thermostable carbonic anhydrase (16). A carbonic anhydrase purified from the archaeon Methanosarcina thermophila is decidedly distinct from the ␣ and ␤ classes, and is the prototype of a different class, the ␥ class (17).Our detection of documented ␤ and ␥ carbonic anhydrases in the methanoarchaea prompted us to investigate the distribution of carbonic anhydrases in the Archaea and Bacteria domains. The results indicate not only that carbonic anhydrases are widely distributed in prokaryotes, but that th...

Structural and Kinetic Characterization of an Archaeal β-Class Carbonic Anhydrase

“…Phe-179 and Tyr-205 form part of an extensive hydrophobic patch whose function may be to ensure that the binding energy of inhibitor molecules is as unfavorable as possible (35). Other members of the same phylogenetic clade as Cab, which consists primarily of sequences from both archaea and grampositive bacteria species, are also missing these active site residues present in P. sativum (51,52). In Cab, Gln-151, Phe-179, and Tyr-205 of the P. sativum enzyme are substituted for by histidine (His-23), lysine (Lys-53), and valine (Val-72), respectively (Fig.…”

“…The most recently identified class of carbonic anhydrase, the ␥-class (24), is represented by the prototype Cam from the archaeon Methanosarcina thermophila (2). Even though sequences encoding putative ␥-class carbonic anhydrases have been found in prokaryotes from both the Bacteria and Archaea domains (2,52), Cam is the only ␥-class enzyme that has been biochemically characterized (2,3,58).…”

“…Only two ␤-class carbonic anhydrases from the Bacteria domain have been purified (22,53), and the subsequent purification of Cab, a ␤-class enzyme from the thermophilic archaeon M. thermoautotrophicum, establishes that this class of carbonic anhydrase extends to the Archaea domain (50). Recent work establishes that this class is widely distributed in metabolically diverse prokaryotes representing both the Bacteria and Archaea domains and has ancient origins (50,52).…”

Malaria parasite carbonic anhydrase: inhibition of aromatic/heterocyclic sulfonamides and its therapeutic potential

“…The enzyme carbonic anhydrase has been identified in all organisms so far examined: animals, plants, yeast, archaea and bacteria [12][13][14][15][16] . The毩-CA isozymes of mammals, in particular the human and bovine, have been thoroughly investigated [17][18][19][20][21] .…”

“…This reaction can occur in the absence of a catalyst but it is too slow [17][18][19] . CA was first purified from bovine red cells in 1933 [12] , followed by the identification of several isozymes ubiquitously distributed in all organisms so far examined [13][14][15][16][17][18][19] . The CAs in protozoa and helminthes parasites are found sparsely [24][25][26][27][28] .…”