Complementation of the yeast deletion mutant ΔNCE103 by members of the β class of carbonic anhydrases is dependent on carbonic anhydrase activity rather than on antioxidant activity

In recent years, members of the class of CAs (carbonic anhydrases) have been shown to complement DeltaNCE103, a yeast strain unable to grow under aerobic conditions. The activity required for complementation of DeltaNCE103 by tobacco chloroplast CA was studied by site-directed mutagenesis. E196A (Glu(196) -->. Ala), a mutated tobacco CA with low levels of CA activity, complemented DeltaNCE103. To determine whether restoration of DeltaNCE103 was due to residual levels of CA activity or whether it was related to previously proposed antioxidant activity of CAs [Gotz, Gnann and Zimmermann (1999) Yeast 15, 855-864], additional complementation analysis was performed using human CAII, an a CA structurally unrelated to the P class of CAs to which the tobacco protein belongs. Human CAII complemented DeltaNCE103, strongly arguing that CA activity is responsible for the complementation of DeltaNCE103. Consistent with this conclusion, recombinant NCE103 synthesized in Escherichia coli shows CA activity, and DeltaNCE103 expressing the tobacco chloroplast CA exhibits the same sensitivity to H2O2 as the wild-type strain.