Expression and characterization of calmodulin-activated (type I) adenylylcyclase

A complementary DNA that encodes a bovine brain, calmodulin-sensitive (type I) adenylylcyclase has been inserted into the baculovirus genome under the control of the strong polyhedron promoter. Expression of the recombinant adenylylcyclase in Sf9 cells using recombinant baculovirus increases adenylylcyclase activity in cell membranes to 10-20 nmol·min^-1·mg^-1 (approximately 0.1% of membrane protein). The catalytic activity of the recombinant adenylylcyclase can be stimulated by G_sα, calmodulin, or forskolin, and it can be inhibited by adenosine analogs and by G protein βγ subunits. The specific activity of the purified recombinant protein approximates 5 μmol·min^-1·mg^-1. This is similar to that of the enzyme purified from bovine brain. Type I adenylylcyclase has a quasiduplicated structure. There are two membrane-spanning domains, each with six putative transmembrane helices, and there are two presumed nucleotide-binding domains that are about 55% similar to each other. No catalytic activity is detectable when each half of the adenylylcyclase molecule is expressed by itself. However, coexpression of the two halves results in considerable enzymatic activity. Interaction between the two halves of adenylylcyclase may be necessary for catalysis.