A role of Anabaena sensory rhodopsin transducer (ASRT) in photosensory transduction

Abstract

SummaryIn 2003, Anabaena sensory rhodopsin (ASR), a membrane-bound light sensor protein, was discovered in cyanobacteria. Since then, a large number of functions have been described for ASR, based on protein biochemical and biophysical studies. However, no study has determined the in vivo mechanism of photosensory transduction for ASR and its transducer protein (ASRT). Here, we aimed to determine the role of ASRT in physiological photoregulation. ASRT is known to be related to photochromism, because it regulates the expression of phycocyanin (cpc-gene) and phycoerythrocyanin (pec gene), two major proteins of the phycobilisome in cyanobacteria. By examining wild type and knockout mutant Anabaena cells, we showed that ASRT repressed the expression of these two genes. We also demonstrated physical interactions between ASRT, ASR, and the promoter regions of cpc, pec, kaiABC (circadian clock gene) and the asr operon, both in vitro and in vivo. Binding assays indicated that ASRT had different sites of interaction for binding to ASR and DNA promoter regions. ASRT also influenced the retinal re-isomerization rate in dark through a physical interaction with ASR, and it regulated reporter gene expression in vivo. These results suggested that ASRT relayed the photosignal from ASR and directly regulated gene expression.

DNA binding activity of Anabaena sensory rhodopsin transducer probed by fluorescence correlation spectroscopy

“…1) While the details of the signal transduction cascade remains to be explored, regulation of the several related genes is suggested as the functional role of ASRT due to its binding ability to DNA. 5,6) Proteins structurally homologous to ASRT are found in clusters with the encoding proteins involved in sugar metabolism, as well as with other membrane proteins related to bioenergetics. 4,7) Also, ASRT is a member of a novel superfamily of β-sandwich fold domain including the sugar-binding site.…”

“…In our previous study, by means of various biochemical methods, we showed evidences of DNA binding activity as a potential gene regulator. 6) Here, we elucidate and characterize the molecular details of ASRT/DNA interaction with different sequences of possible targets in the signal cascade or with random/artificial sequences.…”

Bioinformatic analysis of the distribution of inorganic carbon transporters and prospective targets for bioengineering to increase Ci uptake by cyanobacteria

“…In vitro and in vivo assessments of the interaction between the ASR and ASRT and an increased photocycling rate of ASR in the presence of ASRT confirmed its function as a sensory rhodopsin (Jung et al 2003). It has been recently demonstrated that ASRT relays the signal from ASR and regulates expression of genes such as those coding for phycocyanin, phycoerythrocyanin, and circadian clock proteins by binding to the promoter regions of the respective genes (Kim et al 2014). In contrast, the Gloeobacter violaceus rhodopsin (GvR) was hypothesized to aid in photosynthetic energy production through light-driven proton pumping in this basal cyanobacterium that lacks thylakoids (Miranda et al 2009).…”

Advanced solid-state NMR techniques for characterization of membrane protein structure and dynamics: Application to Anabaena Sensory Rhodopsin

“…ASR is unique among the known microbial rhodopsins in that it is believed to be the only rhodopsin to interact with a cytoplasmic soluble transducer (ASRT) (Fig. 1) [19,21,22]. ASR can be overexpressed in Escherichia coli, and reconstituted in lipids at a high protein-to-lipid ratio in a fully functional state.…”