Ocular Proteins Flashcards
midterm 1
Crystallin’s general info
group of water-soluble protein found in the epithelial and fiber cells of the ocular lens
3 types: alpha, beta & gamma crystallins
crystallins role in the eye
maintain shape of the lens, affect how light is refracted in the lens, and act as molecular chaperones
alpha-crystallins
function as a molecular chaperone:
- maintain normal conformation/folding of other crystallins
-inhibit crystallin aggregation, which leads to cataracts
crystallin age-related transformations (5 of them)
phosphorylation, disulfide bond formation, deamidation, peptide bond disruption, & glycation
crystallin transformation results
change the ratio of water soluble to insoluble lens proteins
- cataracts means larger increase in insoluble proteins, decreasing the ratio of soluble: insoluble proteins
how cataracts form?
in normal lens, reactive AA’s are “buried”
when biochemical transformations occur, oxidizable groups are exposed
leads to aggregate formation
nuclear sclerotic cataracts
changes in tryptophan within crystallins
cortical cataracts
increase in membrane permeability of lens fiber cells with age, leads to over hydration, lens swelling and rupture
which forms debris fragments and crystallin aggregates
Rhodopsin protein function
initiates the transduction process of light energy being converted into electrical signaling, in the retina
Rhodopsin protein structure
transmembrane protein, G-protein coupled receptor, % Vit A prosthetic group
what is rhodopsin without Vit A?
Opsin
mucous glycoproteins (mucins)
found in precorneal tear film, associated w/ 2 sublayers within the mucin layer
-glycocalyx layer: membrane-bound mucins
- mucous: free mucins
mucin function
primarily secreted by conjunctival goblet cells
- are a protective barrier for the cornea
conditions that cause irregular mucin
Vit A deficiency, stevens-Johnson syndrome, alkali burns
corneal stroma collagen
contains Type I, V, VI (mainly I)
- type V limits type I diamater, which prevents light scattering
- type VI stabilizes proteogylcans and keratocytes
vitreous humor collagen
contain type II (vitrosin) & IX, which are arranged in parallel orientation across all of the vitreous humor
type IV basement membrane collagen
tissue sheet that supports or separates cells from other noncellular parts of a tissue
- type IV, in bowman’s membrane, descemet’s membrane, lens capsule, and blood vessels
type VII basement membrane collagen
are anchoring fibrils
Ex. extend from corneal epithelium through bowman’s and adheres to the stroma layer
keratoconus
corneal thinning/steepening due to loss of connective proteins & collagen within the cornea
