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Specific residues in the cytoplasmic domain modulate photocurrent kinetics of channelrhodopsin from Klebsormidium nitens.

ABSTRACT: Channelrhodopsins (ChRs) are light-gated ion channels extensively applied as optogenetics tools for manipulating neuronal activity. All currently known ChRs comprise a large cytoplasmic domain, whose function is elusive. Here, we report the cation channel properties of KnChR, one of the photoreceptors from a filamentous terrestrial alga Klebsormidium nitens, and demonstrate that the cytoplasmic domain of KnChR modulates the ion channel properties. KnChR is constituted of a 7-transmembrane domain forming a channel pore, followed by a C-terminus moiety encoding a peptidoglycan binding domain (FimV). Notably, the channel closure rate was affected by the C-terminus moiety. Truncation of the moiety to various lengths prolonged the channel open lifetime by more than 10-fold. Two Arginine residues (R287 and R291) are crucial for altering the photocurrent kinetics. We propose that electrostatic interaction between the rhodopsin domain and the C-terminus domain accelerates the channel kinetics. Additionally, maximal sensitivity was exhibited at 430 and 460?nm, the former making KnChR one of the most blue-shifted ChRs characterized thus far, serving as a novel prototype for studying the molecular mechanism of color tuning of the ChRs. Furthermore, KnChR would expand the optogenetics tool kit, especially for dual light applications when short-wavelength excitation is required.

SUBMITTER: Tashiro R

PROVIDER: S-EPMC7902849 | biostudies-literature | 2021 Feb

REPOSITORIES: biostudies-literature

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Specific residues in the cytoplasmic domain modulate photocurrent kinetics of channelrhodopsin from Klebsormidium nitens.

Tashiro Rintaro R Sushmita Kumari K Hososhima Shoko S Sharma Sunita S Kateriya Suneel S Kandori Hideki H Tsunoda Satoshi P SP

Communications biology 20210223 1

Channelrhodopsins (ChRs) are light-gated ion channels extensively applied as optogenetics tools for manipulating neuronal activity. All currently known ChRs comprise a large cytoplasmic domain, whose function is elusive. Here, we report the cation channel properties of KnChR, one of the photoreceptors from a filamentous terrestrial alga Klebsormidium nitens, and demonstrate that the cytoplasmic domain of KnChR modulates the ion channel properties. KnChR is constituted of a 7-transmembrane domain ...[more]

PMID: 33623126

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Project description:During the evolution of life on Earth, the conquest of land by plants played a pivotal role producing a boost in land biomass, a substantial drop in atmospheric CO2, an increase in oxygen and the emergence of new terrestrial habitats facilitating land colonization by animals. Therefore, the characterization of the molecular mechanisms that allowed plant terrestralization is a cornerstone in evolutionary studies. Viridiplantae or the green lineage is divided into two clades Chlorophyta or green microalgae and Streptophyta that in turn splits into Embryophyta or land plants and Charophyta. The latest are mainly considered aquatic algae although some facultative terrestrial species has been identified. Charophyta are generally accepted as the extant algal species most closely related to current land plants and, therefore, they are used in evolutionary studies on plant terrestralization. High light irradiance was one of the major stressors that ancestral charophytic algae needed to overcome during the transition from aquatic to terrestrial environments. In this study, we have chosen the facultative terrestrial early charophytic alga Klebsormidium nitens to perform an integrative transcriptomic and metabolomic analysis under high light in order to unveil key mechanisms involved in the early steps of plants terrestralization. We found a fast chloroplast retrograde signaling possibly mediated by reactive oxygen species and the inositol polyphosphate 1-phosphatase (SAL1) and 3′-phosphoadenosine-5′-phosphate (PAP) pathways inducing gene expression and accumulation of specific metabolites. Systems used by both Chlorophyta and Embryophyta were activated such as the xanthophyll cycle with an accumulation of zeaxanthin and protein folding and repair mechanisms constituted by NADPH-dependent thioredoxin reductases, thioredoxin-disulfide reductases and peroxiredoxins. Similarly, cyclic electron flow, specifically the pathway dependent on Proton Gradient Regulation 5, was strongly activated under high light. We detected a simultaneous co-activation of the non-photochemical quenching mechanisms based on LHC-like Stress Related protein and the photosystem II subunit S that are specific to Chlorophyta and Embryophyta respectively. Exclusive Embryophyta systems for the synthesis, sensing and response to the phytohormone auxin were also activated under high light in Klebsormidium leading to an increase in auxin content with the concomitant accumulation of amino acids such as tryptophan, histidine and phenylalanine.

Project description:In two-component signal transduction, response regulator proteins contain the catalytic machinery for their own covalent phosphorylation and can catalyze phosphotransfer from a partner sensor kinase or autophosphorylate using various small molecule phosphodonors. Although response regulator autophosphorylation is physiologically relevant and a powerful experimental tool, the kinetic determinants of the autophosphorylation reaction and how those determinants might vary for different response regulators and phosphodonors are largely unknown. We characterized the autophosphorylation kinetics of 21 variants of the model response regulator Escherichia coli CheY that contained substitutions primarily at nonconserved active site positions D + 2 (CheY residue 59) and T + 2 (CheY residue 89), two residues C-terminal to conserved D57 and T87, respectively. Overall, the CheY variants exhibited a >10(5)-fold range of rate constants (kphos/KS) for reaction with phosphoramidate, acetyl phosphate, or monophosphoimidazole, with the great majority of rates enhanced versus that of wild-type CheY. Although phosphodonor preference varied substantially, nearly all the CheY variants reacted faster with phosphoramidate than acetyl phosphate. Correlation between the increased positive charge of the D + 2 and T + 2 side chains and faster rates indicated electrostatic interactions are a kinetic determinant. Moreover, sensitivities of rate constants to ionic strength indicated that both long-range and localized electrostatic interactions influence autophosphorylation kinetics. The increased nonpolar surface area of the D + 2 and T + 2 side chains also correlated with an enhanced autophosphorylation rate, especially for reaction with phosphoramidate and monophosphoimidazole. Computer docking suggested that highly accelerated monophosphoimidazole autophosphorylation rates for CheY variants with a tyrosine at position T + 2 likely reflect structural mimicry of phosphotransfer from the sensor kinase histidyl phosphate.

Dataset Information

Specific residues in the cytoplasmic domain modulate photocurrent kinetics of channelrhodopsin from Klebsormidium nitens.

Publications

Specific residues in the cytoplasmic domain modulate photocurrent kinetics of channelrhodopsin from Klebsormidium nitens.

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