Covers the over view of Rhodopsin its functions, Four level structure of Rhodopsin, The diseases caused by mutations in the gene, visual signaling( Introduction to GPCR also Included) email- malhotrapurvi24@gmail.com

1. Made By- Purvi Malhotra
Submitted to-Sandeep Sir
Class- BSc.(Hons.)Bioinformatics
Roll no.-2081119
PROTEIN-RHODOPSIN

2. ● Introduction
● What is Rhodopsin?
● Where is rhodopsin found
● Primary function
● Amino acid sequence
● Secondary structure
● Tertiary structure
● Bleaching & Regeneration
● Diseases related to Mutations in rhodopsin : Retinitis Pigmentosa & Congenital
Stationary Night Blindness
● GPCR- Introduction
● Working of rhodopsin i.e. the visual signaling
INDEX:

3. ● The area within the eye that detects light and colour is the called the Retina.
The two types of detection cell present, rods and cones, process information
coming through the Lens and send it down the optic nerve to the brain
● Rod cells (which are around 100 million) detect the degree of lightness
entering the eye and their sensitivity is dependent on the amount of
Rhodopsin present .
● Cone cells (which are around 3 million) are also sensitive to light levels but
retain their function upto high illumination via use of the pigment Iodopsin.
● Detection of colour is a function of the three types of cone cell present
within the retina: between them they cover the visible spectrum
INTRODUCTION

4. ● Rhodopsin was discovered in 1876 by German physiologist Franz Christian
Boll, who observed that the normally reddish purple frog retina turned pale in
bright light
● Rhodopsin is a membrane protein that consists of two parts: the apoprotein,
termed opsin, and the prosthetic group chromophore, 11 cis-retinal
● Rhodopsin (Rho) is a highly specialized G protein-coupled receptor (GPCR)
that detects photons in the rod photoreceptor cell.
● Rhodopsin is an integral membrane protein located in the outer segments of
rod photoreceptor cells in the retina
WHAT IS RHODOPSIN

5. ● It also called visual purple, pigment-containing sensory protein that
converts light into an electrical signal and is required for vision in dim light
● It was the first GPCR to be sequenced, as well as, the first GPCR whose
atomic structure was determined .
● Further, its structure has been crystallized at a relatively high resolution (2.2
Å)
Continued…

6. ● Rhodopsin is a major functional component of photoreceptor rod cells
located in the retinas of vertebrates.(Transmembrane Protein)
● Each rod contains outer segments which consist of 1000-2000 disk
membranes arranged in stacks and surrounded by an outer plasma
membrane.
● The outer segment connects to the inner segment via a ciliary process.
● The disk membranes are the primary cellular location of rhodopsin, and
greater than 90% of the proteins in these membranes are rhodopsin
WHERE IT IS FOUND?

8. ● Rhodopsin is 348 amino acid long protein that crosses the disc membrane
7 times.
● Its mass in 38,893 Da.
● The most prevalent amino acid residues in the primary structure of
rhodopsin (and their relative abundances) are phenylalanine (8.9%),
valine (8.9%), alanine (8.3%), and leucine (8.0%).
● The fact that these residues are all nonpolar correlates well with the high
percentage of the protein that is located within the hydrophobic
membrane bilayers
PRIMARY STRUCTURE

9. MNGTEGPNFYVPFSNATGVVRSPFEYPQYYLAEPWQFSMLAAYMFLLIVLGFPINFLTLY
VTVQHKKLRTPLNYILLNLAVADLFMVLGGFTSTLYTSLHGYFVFGPTGCNLEGFFATLG
GEIALWSLVVLAIERYVVVCKPMSNFRFGENHAIMGVAFTWVMALACAAPPLAGWSRYIP
EGLQCSCGIDYYTLKPEVNNESFVIYMFVVHFTIPMIIIFFCYGQLVFTVKEAAAQQQES
ATTQKAEKEVTRMVIIMVIAFLICWVPYASVAFYIFTHQGSNFGPIFMTIPAFFAKSAAI
YNPVIYIMMNKQFRNCMLTTICCGKNPLGDDEASATVSKTETSQVAPA
AMINO ACID SEQUENCE OF RHODOPSIN

10. ● The first structure of rhodopsin came from cryoelectron microsopy and X- ray
crystallography of bovine rhodopsin from Gebhard Schertler’s group.
● While the resolution of these structures was limited (ranging from 5 to 9Å),
they provided the first picture of the orientation of the TM segments in a lipid
environment.
SECONDARY STRUCTURE OF RHODOPSIN
GERBHARD SCHERTLER

11. ● Helices constitute the majority (60%, 211 residues) of rhodopsin’s secondary structure.
Beta-sheets account for only 2% (10 residues).
● The remaining 38% of residues form random coils
● Rhodopsin consists of three general domains: intracellular, transmembrane, and
extracellular.
● More specifically, each subunit comprises an extracellular N-terminus segment, seven
transmembrane segments (TM1-TM7), three segments that link TM regions on the
extracellular surface (E1-E3), three segments that link TM regions on the cytoplasmic
surface (C1-C3), a final cytoplasmic segment (C4), and an intracellular C-terminus tail
(2).
SECONDARY STRUCTURE

12. N-Terminal lies on the extracellular side while the C-Terminal lies
on the cytoplasmic side of the discs.

13. ● Rho is the first GPCR for which a crystal structure has been reported. To
obtain crystals, bovine Rho was purified from rod outer segment
membranes and crystalised.
● As mentioned before, Rho comprises three topological domains: the
extracellular surface, the membrane-embedded domain, and the intracellular
surface.
● Because of the location of Rho in the disk membrane of the rod outer
segment, the extracellular domain is sometimes referred to as intradiscal.
● The amino terminus of Rho is extracellular and the carboxyl terminus is
intracellular
TERTIARY STRUCTURE

14. ● The seven transmembrane segments are hydrophobic helices that cross the
membrane at varying angles of tilt.
● The seven transmembrane helices in rhodopsin are not regular alpha helices
● In helices I, IV, V, VI and VII, the bends are associated
with proline residues. The kink in helix I involving Pro-53.
● The carbonyl of Met-49 would normally make a hydrogen bond to the amide
of residue 53, but in this case, it twists away from the helical axis due to close
contacts with the proline side chain
● The psi angle of Met-49 twists to a slightly lower negative value than found
in alpha helices, −24°, and the phi angle of Leu-50 moves to −112°.

15. ● The retinal chromophore binds covalently to Lys-296 in TM7 through a
protonated Schiff base linkage within a largely hydrophobic region..
● The Schiff base counterion is Glu-113 in TM3, located 3.26 Å from the
retinal.

17. ● When the eye is exposed to light, the 11-cis-retinal component of rhodopsin is
converted to all-trans-retinal, resulting in a fundamental change in the configuration of
the rhodopsin molecule.
● The change in configuration initiates a phototransduction cascade within the rod,
whereby light is converted into an electrical signal that is then transmitted along
the optic nerve to the visual cortex in the brain.
● The change in configuration also causes opsin to dissociate from retinal, resulting in
bleaching.
● Bleaching limits the degree to which the rods are stimulated, decreasing their
sensitivity to bright light and allowing cone cells (the other type of photoreceptor in the
retina) to mediate vision in bright environments.
BLEACHING

18. ● All-trans-retinal that is released during bleaching is either stored or changed
back to 11-cis-retinal and transported back to the rods. The latter process,
which is known as recycling, allows for the regeneration of rhodopsin.
● Rhodopsin regeneration takes place in darkness and is central to
dark adaptation, when rhodopsin levels, depleted from bleaching in a brightly
lit environment, gradually increase, enabling rod cells to become increasingly
sensitive to dim light.
REGENERATION

20. ● Retinitis pigmentosa (RP) is a group of eye diseases that affect the retina. The retina,
which is located at the back of the eye, sends visual images to the brain where they are
perceived. The cells in the retina that receive the visual images are called
photoreceptors. (rods and cones)
● In RP, the photoreceptors progressively lose function. Side vision, called peripheral
vision, slowly worsens over time. Night vision is also affected. Central vision typically
declines in the advanced stages of the disease.
● Although the disease worsens over time, most patients retain at least partial vision, and
complete blindness is rare.
● There is currently no known cure or effective treatment for retinitis pigmentosa, but
there are some possible ways to manage the condition.
RETINITIS PIGMENTOSA

21. ● World widely, RP is thought to affect roughly one out of 5,000 people.
● Two distinct mutations affecting codon 135, the arginine to tryptophan (Arg-135-Trp, or R135W) and
the argine to lysine (Arg-135-Lys, or R135L) changes, affecting an amino acid at the cytoplasmic
edge of the third rhodopsin transmembrane helix (H3); and two changes in the second intradiscal
loop (E2), the proline to alanine change at codon 180 (Pro-180-Ala, or P180A) and the glycine to
arginine change at codon 188 (Gly-188-Arg, or G188R) have been associated with RP.
● In the early stages of RP, rods are more severely affected than cones. As the rods die,
people experience night blindness and a progressive loss of the visual field

22. ● The loss of rods eventually leads to a breakdown and loss of cones. In the late stages of
RP, as cones die, people tend to lose more of the visual field, developing tunnel vision.
● They may have difficulty performing essential tasks of daily living such as reading,
driving, walking without assistance, or recognizing faces and objects.
● People have difficulty seeing in dim light as well.

23. There is breakdown of rods as well as cones.

24. ● X-linked congenital stationary night blindness is a disorder of the retina
● People with this condition typically have difficulty seeing in low light (night blindness). They also have
other vision problems, including loss of sharpness (reduced acuity),
severe nearsightedness (high myopia), involuntary movements of the eyes (nystagmus), and eyes
that do not look in the same direction (strabismus). Color vision is typically not affected by this
disorder.
● The vision problems associated with this condition are congenital, which means they are
present from birth. They tend to remain stable (stationary) over time.
● It is of two types : Complete and Incomplete
CONGENTAL STATIONARY NIGHT BLINDNESS

25. ● Mutations in the NYX and CACNA1F genes cause the complete and incomplete forms of
X-linked congenital stationary night blindness, respectively. The proteins produced from
these genes play critical roles in the retina
● the NYX and CACNA1F proteins are located on the surface of light-detecting cells called
photoreceptors
● The NYX and CACNA1F proteins ensure that visual signals are passed from rods and
cones to other retinal cells called bipolar cells, which is an essential step in the
transmission of visual information from the eyes to the brain.

26. ● G-protein-coupled receptors (GPCRs) are the largest and most diverse group of
membrane receptors in eukaryotes.
● These cell surface receptors act like an inbox for messages in the form of light energy,
peptides, lipids, sugars, and proteins.
● G proteins are specialized proteins with the ability to bind the nucleotides guanosine
triphosphate (GTP) and guanosine diphosphate (GDP).
● The G proteins that associate with GPCRs are heterotrimeric, meaning they have
three different subunits: an alpha subunit, a beta subunit, and a gamma subunit. Two
of these subunits — alpha and gamma — are attached to the plasma membrane by
lipid anchors
GPCR - Introduction

27. GPCR’s work as an on and off switch.

28. ● In the outermembrane of rod cell cGMP gated Na+ channel is present.
● When cGMP is bound the channels are open so, Na+ can enter thus
depolarising the membrane.
● When a photon strikes rhodopsin, 11-cis retinal gets isomerised to all trans
and this activates rhodopsin.
● Now, the activated rhodopsin binds Transducin, a trimeric protein, and the G-
alpha moves to another membrane bound protein cGMP phoshodiesterase
(PDE).
WORKING OF RHODOPSIN- VISUAL SIGNALING

29. ● When G-alpha binds PDE converts available supply of cGMP to its non cyclic
form 5’-GMP.
● When cGMP dissociates from Na+channel they close causing
hyperpolarisation of the rod cell membrane, thus sending a signal down the
synapse from where the signal is sent to the brain.

31. BIBLIOGRAPHY:
slidesgo
Sciencedirect.com
Ncbi.nlm.nih.gov
collab.its.virginia.edu
Arvojournals.org
Review biotech
Uniprot
Nature.com
Rroij.com

32. THANK YOU!!