The role of electron transfer in the enzymatic activity of a photoactivable adenylate cyclase.

Abstract

OaPAC is a photoactivated adenylate cyclase (PAC) from the photosynthetic cyanobacterium Oscillatoria acuminata and belongs to a class of photoactive flavoenzymes which are involved in the conversion of ATP (adenosine triphosphate) to the important second messenger cAMP (cyclic adenosine monophosphate). The photoactivation is controlled by a BLUF (Blue Light Sensing Using Flavin) domain; a well-known light-triggered switch present in many biological photoreceptors and able to control photochemical energy into a diverse set of cellular responses (e.g. phototaxis, photophobia, enzyme activity, gene expression). Blue-light excitation of the BLUF domain of OaPAC results in a proton-coupled electron transfer process where the primary electron and proton donor is a tyrosine residue in the vicinity of the flavin. The electron transfer to the flavin is accompanied by a reorganization of its hydrogen bond network, and the induced structural changes are believed to propagate towards the AC domain enabling the conversion of ATP to cAMP. In this work we studied the relation between the electron transfer and the activity of the enzyme using ultrafast and fluorescence spectroscopy as well as differential scanning calorimetry. A.L. acknowledges funding from the Hungarian National Research and Innovation Office (K-137557).