Photocage-initiated time-resolved solution X-ray scattering study of a bacterial photoactivated adenylate cyclase.

cAMP (adenosine 3',5'-cyclic monophosphate) is a key second messenger in numerous signal transduction pathways, regulating various cellular functions, including cell growth and differentiation, gene transcription and protein expression. Modulating its cellular concentration has emerged in the focus of modern optogenetic applications putting forward the photoactivated adenylyl cyclases (PACs) in the optogenetics toolbox. PACs are light-activated enzymes that combine the capacity of a photoreceptor with that of an adenylyl cyclase; the latter being an enzyme responsible for the conversion of ATP (adenosine 5'-triphosphate) to cAMP. We propose to use time-resolved wide-angle X-ray scattering (TR-WAXS) in combination with an established photocaging approach to track in real time the structural changes occurring in the photoactivated adenylyl cyclase from a photosynthetic cyanobacterium (OaPAC) during its catalytic reaction, upon light illumination.