Cloning, expression and purification of the alpha-carbonic anhydrase from the mantle of the Mediterranean mussel, Mytilus galloprovincialis

We cloned, expressed, purified, and determined the kinetic constants of the recombinant alpha-carbonic anhydrase (rec-MgaCA) identified in the mantle tissue of the bivalve Mediterranean mussel, Mytilus galloprovincialis. In metazoans, the alpha-CA family is largely represented and plays a pivotal role in the deposition of calcium carbonate biominerals. Our results demonstrated that rec-MgaCA was a monomer with an apparent molecular weight of about 32 kDa. Moreover, the determined kinetic parameters for the CO2 hydration reaction were k(cat) = 4.2 x 10(5) s(-1) and k(cat)/K-m of 3.5 x 10(7) M-1 x s(-1). Curiously, the rec-MgaCA showed a very similar kinetic and acetazolamide inhibition features when compared to those of the native enzyme (MgaCA), which has a molecular weight of 50 kDa. Analysing the SDS-PAGE, the protonography, and the kinetic analysis performed on the native and recombinant enzyme, we hypothesised that probably the native MgaCA is a multidomain protein with a single CA domain at the N-terminus of the protein. This hypothesis is corroborated by the existence in mollusks of multidomain proteins with a hydratase activity. Among these proteins, nacrein is an example of alpha-CA multidomain proteins characterised by a single CA domain at the N-terminus part of the entire protein.