Light-oxygen-voltage-sensing domain

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A Light-oxygen-voltage-sensing domain (LOV domain) is a protein sensor used by a large variety of higher plants, microalgae, fungi and bacteria to sense environmental conditions. In higher plants, they are used to control phototropism, chloroplast relocation, and stomatal opening, whereas in fungal organisms, they are used for adjusting the circadian temporal organization of the cells to the daily and seasonal periods. They are a subset of PAS domains. [1]

Contents

Chromophore

Common to all LOV proteins is the blue-light sensitive flavin chromophore, which in the signaling state is covalently linked to the protein core via an adjacent cysteine residue. [2] [3] LOV domains are e.g. encountered in phototropins, which are blue-light-sensitive protein complexes regulating a great diversity of biological processes in higher plants as well as in micro-algae. [4] [5] [6] [7] [8] Phototropins are composed of two LOV domains, each containing a non-covalently bound flavin mononucleotide (FMN) chromophore in its dark-state form, and a C-terminal Ser-Thr kinase.

Upon blue-light absorption, a covalent bond between the FMN chromophore and an adjacent reactive cysteine residue of the apo-protein is formed in the LOV2 domain. This subsequently mediates the activation of the kinase, which induces a signal in the organism through phototropin autophosphorylation. [9]

While the photochemical reactivity of the LOV2 domain has been found to be essential for the activation of the kinase, the in vivo functionality of the LOV1 domain within the protein complex still remains unclear. [10]

Fungus

In case of the fungus Neurospora crassa , the circadian clock is controlled by two light-sensitive domains, known as the white-collar-complex (WCC) and the LOV domain vivid (VVD-LOV). [11] [12] [13] WCC is primarily responsible for the light-induced transcription on the control-gene frequency (FRQ) under day-light conditions, which drives the expression of VVD-LOV and governs the negative feedback loop onto the circadian clock. [13] [14] By contrast, the role of VVD-LOV is mainly modulatory and does not directly affect FRQ. [12] [15]

Natural and engineered functions of LOV domains

LOV domains have been found to control gene expression through DNA binding and to be involved in redox-dependent regulation, like e.g. in the bacterium Rhodobacter sphaeroides . [16] [17] Notably, LOV-based optogenetic tools [18] have been gaining wide popularity in recent years to control a myriad of cellular events, including cell motility, [19] subcellular organelle distribution, [20] formation of membrane contact sites, [21] microtubule dynamics, [22] transcription, [23] and protein degradation. [24]

See also

Related Research Articles

<span class="mw-page-title-main">Circadian rhythm</span> Natural internal process that regulates the sleep-wake cycle

A circadian rhythm, or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism and responds to the environment. These 24-hour rhythms are driven by a circadian clock, and they have been widely observed in animals, plants, fungi and cyanobacteria.

<span class="mw-page-title-main">Melanopsin</span> Mammalian protein found in Homo sapiens

Melanopsin is a type of photopigment belonging to a larger family of light-sensitive retinal proteins called opsins and encoded by the gene Opn4. In the mammalian retina, there are two additional categories of opsins, both involved in the formation of visual images: rhodopsin and photopsin in the rod and cone photoreceptor cells, respectively.

<span class="mw-page-title-main">Cryptochrome</span> Class of photoreceptors in plants and animals

Cryptochromes are a class of flavoproteins found in plants and animals that are sensitive to blue light. They are involved in the circadian rhythms and the sensing of magnetic fields in a number of species. The name cryptochrome was proposed as a portmanteau combining the chromatic nature of the photoreceptor, and the cryptogamic organisms on which many blue-light studies were carried out.

Phototropins are photoreceptor proteins that mediate phototropism responses in higher plants. Phototropins can be found throughout the leaves of a plant. Along with cryptochromes and phytochromes they allow plants to respond and alter their growth in response to the light environment. Phototropins may also be important for the opening of stomata and the movement of chloroplasts. These blue light receptors are seen across the entire green plant lineage. When Phototropins are hit with blue light, they induce a signal transduction pathway that alters the plant cells' functions in different ways.

Photoreceptor proteins are light-sensitive proteins involved in the sensing and response to light in a variety of organisms. Some examples are rhodopsin in the photoreceptor cells of the vertebrate retina, phytochrome in plants, and bacteriorhodopsin and bacteriophytochromes in some bacteria. They mediate light responses as varied as visual perception, phototropism and phototaxis, as well as responses to light-dark cycles such as circadian rhythm and other photoperiodisms including control of flowering times in plants and mating seasons in animals.

Retinylidene proteins, are proteins that use retinal as a chromophore for light reception. They are the molecular basis for a variety of light-sensing systems from phototaxis in flagellates to eyesight in animals. Retinylidene proteins include all forms of opsin and rhodopsin. While rhodopsin in the narrow sense refers to a dim-light visual pigment found in vertebrates, usually on rod cells, rhodopsin in the broad sense refers to any molecule consisting of an opsin and a retinal chromophore in the ground state. When activated by light, the chromophore is isomerized, at which point the molecule as a whole is no longer rhodopsin, but a related molecule such as metarhodopsin. However, it remains a retinylidene protein. The chromophore then separates from the opsin, at which point the bare opsin is a retinylidene protein. Thus, the molecule remains a retinylidene protein throughout the phototransduction cycle.

Optogenetics is a biological technique to control the activity of neurons or other cell types with light. This is achieved by expression of light-sensitive ion channels, pumps or enzymes specifically in the target cells. On the level of individual cells, light-activated enzymes and transcription factors allow precise control of biochemical signaling pathways. In systems neuroscience, the ability to control the activity of a genetically defined set of neurons has been used to understand their contribution to decision making, learning, fear memory, mating, addiction, feeding, and locomotion. In a first medical application of optogenetic technology, vision was partially restored in a blind patient.

<span class="mw-page-title-main">PAS domain</span> Protein domain

A Per-Arnt-Sim (PAS) domain is a protein domain found in all kingdoms of life. Generally, the PAS domain acts as a molecular sensor, whereby small molecules and other proteins associate via binding of the PAS domain. Due to this sensing capability, the PAS domain has been shown as the key structural motif involved in protein-protein interactions of the circadian clock, and it is also a common motif found in signaling proteins, where it functions as a signaling sensor.

In molecular biology, an oscillating gene is a gene that is expressed in a rhythmic pattern or in periodic cycles. Oscillating genes are usually circadian and can be identified by periodic changes in the state of an organism. Circadian rhythms, controlled by oscillating genes, have a period of approximately 24 hours. For example, plant leaves opening and closing at different times of the day or the sleep-wake schedule of animals can all include circadian rhythms. Other periods are also possible, such as 29.5 days resulting from circalunar rhythms or 12.4 hours resulting from circatidal rhythms. Oscillating genes include both core clock component genes and output genes. A core clock component gene is a gene necessary for to the pacemaker. However, an output oscillating gene, such as the AVP gene, is rhythmic but not necessary to the pacemaker.

Tryptophan-rich sensory proteins (TspO) are a family of proteins that are involved in transmembrane signalling. In either prokaryotes or mitochondria they are localized to the outer membrane, and have been shown to bind and transport dicarboxylic tetrapyrrole intermediates of the haem biosynthetic pathway. They are associated with the major outer membrane porins and with the voltage-dependent anion channel.

The frequency (frq) gene encodes the protein frequency (FRQ) that functions in the Neurospora crassa circadian clock. The FRQ protein plays a key role in circadian oscillator, serving to nucleate the negative element complex in the auto regulatory transcription-translation negative feedback-loop (TTFL) that is responsible for circadian rhythms in N. crassa. Similar rhythms are found in mammals, Drosophila and cyanobacteria. Recently, FRQ homologs have been identified in several other species of fungi. Expression of frq is controlled by the two transcription factors white collar-1 (WC-1) and white collar-2 (WC-2) that act together as the White Collar Complex (WCC) and serve as the positive element in the TTFL. Expression of frq can also be induced through light exposure in a WCC dependent manner. Forward genetics has generated many alleles of frq resulting in strains whose circadian clocks vary in period length.

White Collar-1 (wc-1) is a gene in Neurospora crassa encoding the protein WC-1. WC-1 has two separate roles in the cell. First, it is the primary photoreceptor for Neurospora and the founding member of the class of principle blue light photoreceptors in all of the fungi. Second, it is necessary for regulating circadian rhythms in FRQ. It is a key component of a circadian molecular pathway that regulates many behavioral activities, including conidiation. WC-1 and WC-2, an interacting partner of WC-1, comprise the White Collar Complex (WCC) that is involved in the Neurospora circadian clock. WCC is a complex of nuclear transcription factor proteins, and contains transcriptional activation domains, PAS domains, and zinc finger DNA-binding domains (GATA). WC-1 and WC-2 heterodimerize through their PAS domains to form the White Collar Complex (WCC).

Steve A. Kay is a British-born chronobiologist who mainly works in the United States. Dr. Kay has pioneered methods to monitor daily gene expression in real time and characterized circadian gene expression in plants, flies and mammals. In 2014, Steve Kay celebrated 25 years of successful chronobiology research at the Kaylab 25 Symposium, joined by over one hundred researchers with whom he had collaborated with or mentored. Dr. Kay, a member of the National Academy of Sciences, U.S.A., briefly served as president of The Scripps Research Institute. and is currently a professor at the University of Southern California. He also served on the Life Sciences jury for the Infosys Prize in 2011.

<span class="mw-page-title-main">FMN-binding fluorescent protein</span>

A FMN-binding fluorescent protein (FbFP), also known as a LOV-based fluorescent protein, is a small, oxygen-independent fluorescent protein that binds flavin mononucleotide (FMN) as a chromophore.


LiMETER stands for light-inducible membrane-tethered peripheral endoplasmic reticulum (ER). LiMETER is an optogenetics tool designed to reversibly label cortical ER or the apposition between plasma membrane (PM) and endoplasmic reticulum (ER) membranes.

<span class="mw-page-title-main">Microbial rhodopsin</span> Retinal-binding proteins

Microbial rhodopsins, also known as bacterial rhodopsins are retinal-binding proteins that provide light-dependent ion transport and sensory functions in halophilic and other bacteria. They are integral membrane proteins with seven transmembrane helices, the last of which contains the attachment point for retinal.

The white collar--2 (wc-2) gene in Neurospora crassa encodes the protein White Collar-2 (WC-2). WC-2 is a GATA transcription factor necessary for blue light photoreception and for regulating circadian rhythms in Neurospora. In both contexts, WC-2 binds to its non-redundant counterpart White Collar-1 (WC-1) through PAS domains to form the White Collar Complex (WCC), an active transcription factor.

Archaerhodopsin proteins are a family of retinal-containing photoreceptors found in the archaea genera Halobacterium and Halorubrum. Like the homologous bacteriorhodopsin (bR) protein, archaerhodopsins harvest energy from sunlight to pump H+ ions out of the cell, establishing a proton motive force that is used for ATP synthesis. They have some structural similarities to the mammalian GPCR protein rhodopsin, but are not true homologs.

Transcription-translation feedback loop (TTFL), is a cellular model for explaining circadian rhythms in behavior and physiology. Widely conserved across species, the TTFL is auto-regulatory, in which transcription of clock genes is regulated by their own protein products.

Jay Dunlap is an American chronobiologist and photobiologist who has made significant contributions to the field of chronobiology by investigating the underlying mechanisms of circadian systems in Neurospora, a fungus commonly used as a model organism in biology, and in mice and mammalian cell culture models. Major contributions by Jay Dunlap include his work investigating the role of frq and wc clock genes in circadian rhythmicity, and his leadership in coordinating the whole genome knockout collection for Neurospora. He is currently the Nathan Smith Professor of Molecular and Systems Biology at the Geisel School of Medicine at Dartmouth. He and his colleague Jennifer Loros have mentored numerous students and postdoctoral fellows, many of whom presently hold positions at various academic institutions.

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