Proteins and eye

Retinal Rhodopsin and its function in the eye, Crystalline proteins and its age-related degeneration, Kwashiorkor and xerophthalmia and other eye problems, Cornea in Kwashiorkor

1. Unit: II
Energy –Units, Metabolisms, Energy expenditure,
and Energy imbalance. Digestion, absorption and
transport of Food Proteins and eye
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2. Unit: II
Proteins and eye
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3. Retinal Rhodopsin
•Retinal rod pigments are more abundant and stable than cone pigments
•visual pigments consist of an apoprotein -opsin to which a chromophore is attached.
•The spectral properties of these visual pigments are largely determined by the retinene
chain of the chromophore
•Rhodopsin is contains the chromophore 11-cis-retinal -an aldehyde derivative of
vitamin A with λ
max = 498nm
•The cone pigments consist of
▪blue sensitive cones (λ
max = 419 nm)
▪green-sensitive cones (λ
max= 531 nm)
▪red-sensitive cones ( λmax = 558 nm)

4. Retinal Rhodopsin
•Rhodopsin is located in
the disc membranes of
the rod outer segments
(ROS) of the
photoreceptor cells of the
retina
•it comprises 80% of total
protein with the other
proteins present involved
in the phototransduction
cascade

5. Retinal Rhodopsin

6. Retinal Rhodopsin
•Rhodopsin is an example of G protein coupled receptors (GPCRs)
•Rhodopsin absorbs radiations of wavelengths in or near the visible part of the
electromagnetic spectrum
•The bleaching pathway involves the isomerisationof the chromophore 11-
cisretinal around the C
11==C
12double bond to form all-trans-retinal.
•The final reaction in the bleaching process involveshydrolysis and dissociation to
all-transretinaldehydeand the apoprotein opsin-a requirement for full
deactivation of light-stimulated photoreceptor cells.
•11-cis-retinal is then regenerated and supplied to opsin by the visual cycle to
restore the dark pigment.

7. Lens Crystalline Proteins
•lens must maintain its own clarity, provide refractive power and absorb ultraviolet
(UV).
•lens is avascular and its protein concentration is the highest of any organ -450
mg/ml
•lens proteins are uniformly packed in high density within the fibrecells
•lens is a growing tissue in which concentric layers of fibrecells continuously overlay
their predecessors.
•outer younger part of the lens is called the cortex and the older core or inner part
is called the nucleus

8. Lens Crystalline Proteins
•lens has a unique growth pattern -no protein turnover in the differentiated fibre
cells and no diffusion of proteins between cells.
•Therefore, proteins synthesized during embryogenesis are still present in fibrecells
located in the core of an aged lens
•vertebrate lens consist mainly of the structural proteins crystallins(90% of total
proteins) which are classified into α, βand ɣ
•they also contain enzymatic proteins, including glyceraldehyde-3P dehydrogenase,
glucose-6P dehydrogenase and enolase.

9. Age and denaturation
•In the nucleus of lens older proteins begin to unfold and denature with age
•Once denatured, the hydrophobic core is exposed; this tends to interact with
exposed hydrophobic regions of other denatured proteins, leading to the
formation of insoluble aggregates.
•Such insoluble protein aggregates cause light-scattering which interferes with lens
transparency and, hence, with vision (cataract).

10. UV light and Cataract
•UV radiation from sunlight is known to cause structural and functional alterations
to lens macromolecules and is one of the major risk factors in the aetiologyof
human cataract formation.
•The lens fibrecells contain a group of UV filter compounds.
•These compounds absorb harmful radiation (295–400 nm), preventing it reaching
the retina, thus increasing visual acuity.
•some UV filters can over time form reactive substances which bind to the
crystallin proteins in human lens, leading to coloration, fluorescence and ultimately
cataract formation.

11. Protein Deficiency
•Kwashiorkor is a form of severe protein
malnutrition characterized by edema, and an
enlarged liver with fatty infiltrates.
•Sufficient calorie intake, but with insufficient
protein consumption, distinguishes it from
marasmus.
•Kwashiorkor cases occur in areas of famine or
poor food supply

12. Kwashiorkor: Symptoms
•The defining sign is pitting edema (swelling of the ankles and feet).
•A distended abdomen, an enlarged liver with fatty infiltrates, thinning of hair,
loss of teeth, skin depigmentation and dermatitis.
•Often develop irritability and anorexia.
•the disease can be treated by adding protein to the diet -it can have a long-term
impact on a child's physical and mental development and in severe cases may
lead to death.
•marasmusis the more frequent disease associated with malnutrition. Cachexia is
also associated

13. Xerophthalmia and Kwashiorkor
•Xerophthalmiais a medical condition in which the eye fails to produce tears. It
may be caused by vitamin A deficiency
•The conjunctiva becomes dry, thick and wrinkled. If untreated, it can lead to
corneal ulceration and ultimately to blindness as a result of corneal damage
•Xerophthalmia can be caused vitamin A deficiency
•In Kwashiorkor severe protein deficiency lead to deficiency of Retinol binding
protein (RBP) that can lead to vit A deficiency
•In such cases the patient will show vitamin A deficiency but will not respond to vit
A supplementation

14. Xerophthalmia and Kwashiorkor

15. Xerophthalmia and Kwashiorkor
•Xerophthalmia is found associated with Kwashiorkor in several African and Asian
countries
•Children with concurrent severe protein deficiency should receive an additional
oral dose every two weeks until their protein status improves

16. Cornea in Kwashiorkor
•resistance of the cornea to infection is lowered in Kwashiorkor
•The Lowering of resistance of the cornea to infection must be
explained on the basis of the histopathological change brought
about by the state of malnutrition
•humoral defense reaction is impaired in Kwashiorkor
•The eye has poor inflammatory vascular response in the presence of
a severe corneal ulcer

17. Cornea in Kwashiorkor
•The normal corneal epithelium acts as a defense barrier against bacterial
infection by imperviousness of its cells.
•With the exception of gonococci, diphtheria bacilli, and viruses, the intact
corneal epithelium is impervious to bacterial toxins ordinarily present.
•But in Kwashiorkor this barrier is weakened, as the corneal epithelium is
thinned by atrophy,the cells are abnormal and may be keratinized
•Epithelial abrasions, which commonly occur in severe Kwashiorkor, may
permit the entry of bacteria, thus rendering the cornea more liable to
infection.

18. Other conditions related to Kwashiorkor
•Night blindness: Several studies indicate that night blindness is
associate with protein energy malnutrition. In a study by Hussain
et.al*, mid-upper arm circumference (MUAC) of Bangladeshi
children had a direct correlation with night blindness.
*Protein energy malnutrition, vitamin A deficiency and night blindness in Bangladeshi children. Hussain
A(1), LindtjørnB, KvåleG, Ann Trop Paediatr. 1996 Dec;16(4):319-25. PMID: 8985529

19. Other conditions related to Kwashiorkor
•Keratomalaciais most frequently caused by prolonged dietary deprivation of
vitamin A (i.e., primary vitamin A deficiency).
•Primary vitamin A deficiency is common in certain regions where rice is a major
component of the diet (e.g., eastern and southern Asia); rice does not contain
beta-carotene, which is converted by the body into vitamin A.
•In addition, keratomalacia is common with certain malnutrition disorders
resulting from insufficient consumption of protein and energy (i.e., protein-
calorie malnutrition, such as kwashiorkor).
•In such cases, vitamin A deficiency may result from dietary deprivation as well as
defective storage and transport of vitamin A.
•Keratomalacia occurs most commonly in developing countries due to prolonged
dietary deprivation of vitamin A or protein-calorie malnutrition.