Abstract
Carbonic anhydrases (CAs) are metalloenzymes that are omnipresent in nature. CAs catalyze the basic reaction of the reversible hydration of CO2 to HCO3− and H+ in all living organisms. Photosynthetic organisms contain six evolutionarily different classes of CAs, which are namely: α-CAs, β-CAs, γ-CAs, δ-CAs, ζ-CAs, and θ-CAs. Many of the photosynthetic organisms contain multiple isoforms of each CA family. The model alga Chlamydomonas reinhardtii contains 15 CAs belonging to three different CA gene families. Of these 15 CAs, three belong to the α-CA gene family; nine belong to the β-CA gene family; and three belong to the γ-CA gene family. The multiple copies of the CAs in each gene family may be due to gene duplications within the particular CA gene family. The CAs of Chlamydomonas reinhardtii are localized in different subcellular compartments of this unicellular alga. The presence of a large number of CAs and their diverse subcellular localization within a single cell suggests the importance of these enzymes in the metabolic and biochemical roles they perform in this unicellular alga. In the present review, we update the information on the molecular biology of all 15 CAs and their metabolic and biochemical roles in Chlamydomonas reinhardtii. We also present a hypothetical model showing the known functions of CAs and predicting the functions of CAs for which precise metabolic roles are yet to be discovered.
Highlights
Carbonic anhydrases (EC 4.2.1.1) (CAs) are metalloenzymes that catalyze the reversible reaction of hydration of carbon dioxide to bicarbonate (CO2 + H2 O ⇔ HCO3 − + H+ )
The presence of 15 CAs in C. reinhardtii suggests that they are involved in several other metabolic functions in addition to a CO2 -concentrating mechanism (CCM), which is attributed to the evolutionarily conserved enzymes in plants
The diversity in location suggests the importance of the CAs in the many physiological and biochemical roles they may play in photosynthetic organisms
Summary
Carbonic anhydrases (EC 4.2.1.1) (CAs) are metalloenzymes that catalyze the reversible reaction of hydration of carbon dioxide to bicarbonate (CO2 + H2 O ⇔ HCO3 − + H+ ). The presence of 15 CAs in C. reinhardtii suggests that they are involved in several other metabolic functions in addition to a CO2 -concentrating mechanism (CCM), which is attributed to the evolutionarily conserved enzymes in plants. We will describe the information that is available on the molecular biology, and present the data for the metabolic and biochemical roles of the three CA gene families. We will present a hypothetical model showing the known functions of CAs and predicting the functions of CAs for which precise metabolic roles are yet to be discovered. We present future directions in the field of C. reinhardtii CA research in order to study the precise metabolic and physiological roles of CAs from this alga
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