Structural basis of adenylyl cyclase 9 activation

Adenylyl cyclase 9 (AC9) is a membrane-bound enzyme that converts ATP into cAMP. The enzyme is weakly activated by forskolin, fully activated by the G protein G alpha s subunit and is autoinhibited by the AC9 C-terminus. Although our recent structural studies of the AC9-G alpha s complex provided the framework for understanding AC9 autoinhibition, the conformational changes that AC9 undergoes in response to activator binding remains poorly understood. Here, we present the cryo-EM structures of AC9 in several distinct states: (i) AC9 bound to a nucleotide inhibitor MANT-GTP, (ii) bound to an artificial activator (DARPin C4) and MANT-GTP, (iii) bound to DARPin C4 and a nucleotide analogue ATP alpha S, (iv) bound to G alpha s and MANT-GTP. The artificial activator DARPin C4 partially activates AC9 by binding at a site that overlaps with the G alpha s binding site. Together with the previously observed occluded and forskolin-bound conformations, structural comparisons of AC9 in the four conformations described here show that secondary structure rearrangements in the region surrounding the forskolin binding site are essential for AC9 activation.

Automated summary

Adenylyl cyclase 9 (AC9) is an enzyme that converts ATP to cAMP, activated weakly by forskolin and fully by G protein G alpha s subunit, and autoinhibited by AC9 C-terminus. Cryo-EM structures of AC9 in different states show that conformational changes in the region surrounding the forskolin binding site are essential for AC9 activation, with an artificial activator DARPin C4 partially activating AC9 by binding at a site overlapping with G alpha s binding site.