Retinal Photoreceptor Rhodopsin: A G-Protein Receptor Essay examples

After a retinal molecule absorbs light, the normally 11-cis form of the bound retinal molecule straightens to become the 11-trans from. This change activated the opsin molecule. Opsin activates transducin which is a G protein. This G protein then activates phosphodiesterase. Phosphodiesterase is an enzyme that breaks down cyclic-GMP. The break-down of cyclic-GMP removes them from the gated sodium channels and makes the gated sodium channels inactive. Because of this, sodium ion entry into the cytoplasm decreases.

Retinitis pigmentosa is a group of inheritable diseases that is characterized by gradual deterioration of the photoreceptors in the retina. The photoreceptor cells in the retina, rod cells, are light sensitive cells that are able to sense low levels of light. The frequency of retinitis pigmentosa is one in four thousand births (Deng et al., 2015; Fahim et al., 2012; Haddad et al., 2016; Shu et al., 2012) People affected by retinitis pigmentosa will typically exhibit symptoms of night-blindness first, and this will precede a loss in the patient’s visual acuity field that starts from the outer edge and gradually moves inward resulting in a much smaller visual field and loss of peripheral vision, also known as tunnel vision (Haddad et al., 2016).

To understand the diverse causes of RP, a basic understanding of visual perception is required. Phototransduction (conversion of light to electrical signals) occurs first, which is initiated by two types of photoreceptors: rods and cones. These two types vary in their function as rods are primarily responsible for night vision and lack sensitivity to color while cones function in color vision. Light contacts these photoreceptors, and isomerizes a retinaldehydechromophore (retinal) which is bound to varying types of opsin proteins corresponding in their reactivity to different wavelengths of light. Upon absorption of a photon of light, the chromophore 11-cis-retinal is isomerized to the all-trans confirmation, which subsequently causes a series of molecular interactions which ultimately result in the electrical response of the photoreceptors (Vugler 2010). As 11-cis-retinal is required to absorb photons of light, this compound must be regenerated, a function that is performed with the aid of nearby cells of the retinal pigment epithelium

They hypothesized that inserting GFP into the S3-S4 loop would allow voltage-induced movements to interrupt GFP fluorescence. They also hypothesized that a VSD with a shorter loop would increase the coupling between the voltage-induced movements and GFP barrel distortions. They performed various tests and concluded that a particular variant of the GFP improved brightness, dynamic range and expression at the membrane, giving rise to the protein they named ASAP1. From here they performed tests to show that the VSD that they chose initially was the best choice.

The association between Arginine vasopressin and visual processing is one of the least studied regions when it comes to AVP and sensory integration links although many visual inputs enter brain regions which are comprised of vasopressin receptors. One of the few studies that research this link includes an exploration of visual opsin sequences in diverse vertebrate animals. The researchers claimed that the visual opsins and AVP receptors are located together in the same genomic region(130). For instance, in chickens, it was claimed that a visual opsin was sharing a genomic region with AVT in the neurons. Nonetheless, even though the other functions of opsins besides the visual ones are still unknown, a study performed in Japan hypothesize that the pigments are permitting the neurons to react to light and contribute with coordination of behavior (Bester et al. 2015).

Detection of visual stimuli relies on an intact neural pathway beginning with retinal photoreceptors, and then proceeding through bipolar cells, retinal ganglion cells (RGC), and brain neurons extending from the lateral geniculate to the occipital cortex.

For the second part of the experiment, one had to use the knowledge learn from viewing protein molecules in FirstGlance in Jmol to analyze the protein PDB ID: 4EEY. The analysis of this protein was done using the RSCB protein data bank (PDB) at (http://www.rcsb.org/pdb/home/home.do).2

There are three kinds of genes that provide proteins that make up color vision: OPN1LW, OPN1MW and OPN1SW. (Hunt et al. 1995) These genes are found in the retina and are made up of different light receptor cells called rods and cones. (Hunt et al. 1995; Nathans et al. 1986)

Rhodopsin is a biological pigment which is extremely sensitive to light energy found in the rods of the retina and is said to be a G-protein-coupled receptor (GPCR). It was discovered that when rhodopsin is exposed to light energy, it immediately photobleaches.

This article discusses optogenetic inhibition, which is the use of light-activated ion pumps to enable transient activity suppression of genetically targeted neurons by pulses of light. The created silencer ‘Jaws’ results in red light-induced photocurrents three times those of earlier silencers. This red-shifted variant can help solve known issues associated with implants, as it is a non-invasive method. Similar to previously mentioned papers focusing optogenetic excitation, this article will be used to provide more information about ChR variants and provides the basic knowledge to understand neuronal silencing as it is used in studies regarding optogenetics and Parkinson’s disease.

This is identified as a tetramer with 1023 amino acids residues in each subunit with their own active sites (Juers et al., 2012). As shown in Figure 2, 12% of the molecule is of helical (20 helices; 130 residues) and 41% is comprised of beta sheet (77 strands; 423 residues) (Juers et al., 2012). The first beta strand begins on the 22nd residue and the 39th encloses the first alpha helix strand (Juers et al., 2012). Within each monomer, the amino acids form 5 structural domains as shown in Figure 3. Domain 1 is a jelly-roll type barrel, domain 2 and 4 are fibronectin type III-like barrels and domain 5 is a β-sandwich (Jacobson and Matthews, 1992). The third (central domain) contains the active site which forms a deep pit at the C-terminal end of the barrel made up of 334-627 residues and is a triose phosphate isomerase (Jacobson and Matthews,

The primary protein structure can be likened to a human chain in which each person is assumed to be an amino acid and their hands viewed as the carboxyl and amino groups. The person on one end of the chain, who has a free left hand, is assumed to be the free carboxyl group. The person on the other end, who has a free right hand, is assumed to be the free amino group. Everyone in this chain has a left hand linked to somebody’s right hand and a right hand linked to somebody else’s left hand forming peptide bonds. The heads and legs just like the side chains and hydrogens, do not take part in the linking.

In the field of neuroscience, the endeavor to develop technologies that allow minimally invasive, temporally and spatially precise, and genetically specific neural activation has occupied the minds of neuroscientists for decades. To this end, photostimulation techniques have been of particular interest. In the early 2000s, a set of light-gated proteins called channelrhodopsins (ChRs) from the green alga Chlamydomonas reinhardtii were characterized1,2 and noted for their potential ability to depolarize cells in other biological systems. In particular, channelrhodopsin 2 (ChR2), a light-gated nonselective-cation channel, has proven to be immensely useful. The genes expressing these photoreceptors have been used to introduce light-activated channels into selective cell populations of vertebrates to optically induce neural activity3.

Several researchers like (Burakova and Mazokhin-Porshnyakov, 1982; Mishra and Meyer-Rochow, 2008a) confirmed that the vesicles originate from inflation of the interretinular strands and are simply extensions of the cone cells. Shaw (1978) considered the presence of vesicles around the rhabdomere to be a typical feature of dark/light adaption. The location of the interretinular spaces suggests two possible functions. The first is to make physical contact with the rhabdomeres because both of them disappear in the nuclear region. The second, physiological function by increase sensitivity at the cost of resolution the presence of a palisade, which bodice the pigment granules away from the rhabdom. Finally, accordingly to (Horridge and Barnard, 1965) this IRSs have a light-guiding function apparently to protect the photoreceptors from damage by the allowing of stray light to entire the eyes.

The phototransduction cascade converts light into electrical signals in the rod and cone cells, and in the photosensitive ganglion cells of the retina of the eye. This biological cycle converts photons into electrical signals in the retina. Rod photoreceptors in vertebrates are responsible for initiating vision by allowing light to isomerize 11-cis retinal chromophore of rhodopsin. This results in the rhodopsin to be excited and activates transducin to stimulate cCMP hydrolysis by the PDE, leading to less cGMP in the outer segment of photoreceptors. The decrease in cGMP closes channels, which haults the entry of sodium and calcium. This will lead to a hyperpolarized cell, as well as reducing the synaptic release of neurotransmitter glutamate.