Signal transduction in light-oxygen-voltage receptors lacking the active-site glutamine

Abstract

In nature as in biotechnology, light-oxygen-voltage photoreceptors perceive blue light to elicit spatiotemporally defined cellular responses. Photon absorption drives thioadduct formation between a conserved cysteine and the flavin chromophore. An equally conserved, proximal glutamine processes the resultant flavin protonation into downstream hydrogen-bond rearrangements. Here, we report that this glutamine, long deemed essential, is generally dispensable. In its absence, several light-oxygen-voltage receptors invariably retained productive, if often attenuated, signaling responses. Structures of a light-oxygen-voltage paradigm at around 1 Å resolution revealed highly similar light-induced conformational changes, irrespective of whether the glutamine is present. Naturally occurring, glutamine-deficient light-oxygen-voltage receptors likely serve as bona fide photoreceptors, as we showcase for a diguanylate cyclase. We propose that without the glutamine, water molecules transiently approach the chromophore and thus propagate flavin protonation downstream. Signaling without glutamine appears intrinsic to light-oxygen-voltage receptors, which pertains to biotechnological applications and suggests evolutionary descendance from redox-active flavoproteins.

Light-regulated gene expression in Bacteria: Fundamentals, advances, and perspectives

“…The resultant flavin protonation is read out by a conserved glutamine and transduced in form of hydrogen-bonding rearrangements. Intriguingly, neither the cysteine (Yee et al, 2015) nor the glutamine (Dietler et al, 2022) are strictly required for signal transduction; their removal can modulate the absolute light sensitivity and dark recovery of the receptor but generally impairs the fidelity of signaling. With certain exceptions (Rivera-Cancel et al, 2014), bacterial LOV receptors are parallel homodimers that exhibit a range of associated effector modules (Glantz et al, 2016).…”

“…The targeted variation of recovery kinetics thus provides a handle to substantially modulate the sensitivity of optogenetic circuits at photostationary state (Ziegler and Möglich, 2015;Hennemann et al, 2018). However, caution must be exerted, as certain residue exchanges were found to not only modulate the recovery kinetics but to also negatively affect signal transduction e.g., (Diensthuber et al, 2014;Dietler et al, 2022).…”

“…Although most pertinent setups achieve optogenetic regulation via light-dependent dimerization and dissociation reactions, the pioneering LOV-TAP system does not but relies on other modes of allostery (Strickland et al, 2008). This system harnesses the widely used AsLOV2 module which undergoes reversible unfolding of its N-terminal A'α and C-terminal Jα helices under blue light (Harper et al, 2003;Zayner et al, 2012;Dietler et al, 2022). Within LOV-TAP, the AsLOV2 domain is fused to the E. coli tryptophan repressor (TrpR) such that the Jα helix overlaps in sequence with an N-terminal helix of TrpR.…”

Light-dependent Control of Bacterial Expression at the mRNA Level

“…The fractional populations f of the different activity states of the integrated circuit are given by eqs. (3)(4)(5)(6).…”

“…Light absorption by a flavin-nucleotide chromophore within the LOV sensor initiates a wellcharacterized photocycle during which a conserved cysteine residue covalently bonds to the atom C4a of the flavin isoalloxazine heterocycle 3 . This reaction is accompanied by protonation of the neighboring flavin N5 atom which triggers hydrogen-bonding and conformational rearrangements and thereby converts the photosensory input into biochemical signal outputs [4][5][6] . The underlying structural transitions propagate from the LOV sensor to the effector module via linker segments that are frequently α-helical in structure.…”