A ternary AppA–PpsR–DNA complex mediates light regulation of photosynthesis-related gene expression

Abstract

The anoxygenic phototrophic bacterium Rhodobacter sphaeroides uses different energy sources depending on environmental conditions including aerobic respiration or, in the absence of oxygen, photosynthesis. Photosynthetic genes are repressed at high oxygen tension, but at intermediate levels their partial expression prepares the organism for using light energy. Illumination, however, enhances repression under semi-aerobic conditions. Here, we describe molecular details of two proteins involved in oxygen- and light-control of photosynthesis gene expression, the light-sensing anti-repressor AppA and the transcriptional repressor PpsR. We combine information from crystal structures of both proteins and their complex with hydrogen-deuterium exchange data to show that light-activation of AppA–PpsR2 affects the PpsR effector region within the complex. DNA-binding studies demonstrate the formation of a light-sensitive ternary AppA–PpsR–DNA complex. Implications of these results for light- and oxygen-regulation are discussed, highlighting new insights into blue-light-mediated signal transduction.

Optogenetic Module for Dichromatic Control of c-di-GMP Signaling

“…We expressed this fragment in a highly motile strain, MG1655, and analyzed its ability to inhibit swimming in semisolid agar but observed no decrease, regardless of oxygen levels (data not shown), suggesting that the PAS9-GGDEF fragment in itself is insufficient for DGC activity. It would be insightful to decipher how oxygen and light affect the enzymatic activities of the Bldp proteins; however, such studies are challenging, and even the best-understood dual (oxygen and light)-sensing proteins remain only partially characterized (42)(43)(44)(45)(46).…”

Members of the PpaA/AerR Antirepressor Family Bind Cobalamin

“…The location where His binds Co in PpsR/AerR has also been replaced with a Pro in AppA, and the canonical Gly in PpsR/AerR has been replaced with a bulky charged Glu in AppA. Recent crystal structures of the AppA SCHIC domain show that the presence of a Glu at the terminal position of this motif may be providing electrostatic repulsion to the phosphate group in cobalamin, thereby affecting binding to this tetrapyrrole (23,28). When we introduced a Gly-to-Glu mutation at the terminal position of this motif in PpaA, it indeed resulted in loss of cobalamin binding and a slight increase in heme binding.…”

“…strain ORS278 is inhibited by a lightregulated interaction with the red-light-absorbing phytochromelike photoreceptor BphB2 (11). In Rhodobacter sphaeroides, the activity of PpsR is inhibited by an interaction with the antirepressor AppA that converts PpsR from an active tetramer to an inactive dimer (17,(23)(24)(25). The antirepressor activity of AppA is reg-ulated by both blue light absorption via a bound flavin and the presence of a bound heme (17,(26)(27)(28).…”

LOV and BLUF flavoproteins’ regulatory photoreceptors of microorganisms and photosensory actuators in optogenetic systems

“…Кроме того, продемонстрировано формирование светочувствительного тройного комплекса AppAPpsR -DNA, через который может передаваться сигнал посредством аллостерических структурных изменений. Согласно предложенному механизму, фотомодифицированный комплекс AppA -PpsR 2 взаимодействует с сайтами связывания PpsR на ДНК, предотвращая формирование PpsR-DNA-репрессорного комплекса, что приводит к актива-ции экспрессии фотосинтетических генов [14].…”

“…Взаимодействие комплекса AppA -PpsR с сайтами связыва-ния репрессора PpsR на ДНК предотвращает формирование PpsR -ДНК-репрессорного комплекса [14] Активация экспрессии фотосинтетических ге-нов. Синтез компонентов аппарата фотосинтеза у R. sphaeroides [6,14] bPAC (BLUF -AC)…”