The evolution of metazoan α-carbonic anhydrases and their roles in calcium carbonate biomineralization

The carbonic anhydrase (CA; EC 4.2.1.1) superfamily is a class of ubiquitous metallo-enzymes that catalyse the reversible hydration of carbon dioxide. The ?-CA family, present in all metazoan clades, is a key enzyme involved in a wide range of physiological functions including pH regulation, respiration, photosynthesis, and biocalcification. This paper reviews the evolution of the ?-CA family, with an emphasis on metazoan ?-CA members involved in biocalcification. Phylogenetic analyses reveal a complex evolutionary history of ?-CAs, and suggest ?-CA was independently co-opted into a variety of skeleton forming roles (e.g. as a provider of HCO3? ions, a structural protein, a nucleation activator, etc.) in multiple metazoan lineages. This evolutionary history is most likely the result of multiple gene duplications coupled with the insertion of repetitive or non-repetitive low-complexity domains (RLCDs/LCDs). These domains, of largely unknown function, appear to be lineage-specific, and provide further support for the hypothesis of independent recruitment of ?-CAs to diverse metazoan biocalcification processes. An analysis of ?-CA sequences associated with biocalcification processes indicates that the domains involved in the activity and conformation of the active site are extremely conserved among metazoans.PhD Fellowship from the Ministère de l' Education Nationale et de la Recherche (contract number 27264–2007), ANR project (ACCRO-Earth, ref. BLAN06-2_159971, coordinator Gilles Ramstein, LSCE, Gif/Yvette, France) for years 2007–2011, SU (INTERRVIE project year 2010), COST network TD0903 "Biomineralix", ECTS (internship grant, 2012)