Functional chimeras between the catalytic domains of the mycobacterial adenylyl cyclase Rv1625c and a Paramecium guanylyl cyclase.

The class IIIa adenylyl cyclase (AC) Rv1625c from Mycobacterium tuberculosis forms homodimers with two catalytic centres, whereas the Paramecium guanylyl and mammalian ACs operate as pseudoheterodimers with one catalytic centre. The functional and structural relationship of the catalytic domains of these related class III cyclases was investigated. Point mutations introduced into Rv1625c to engineer a forskolin-binding pocket created a single heterodimeric catalytic centre, yet did not result in forskolin activation. Chimerization of these Rv1625c point mutants with corresponding mammalian AC domains was impossible. However, it was successful using a complemental Paramecium guanylyl cyclase domain and resulted in an AC. The data signify a divergence of structural and functional evolution in class III Acs.