The extracellular Matrix Flashcards
Major constituents of the ECM
- Collagen fibers
- Elastic fibers
- Proteogylcans and hyaluronic acid
- Glycoproteins
What gives the tissue tensile strength?
Collagen fibers
What gives the elasticity to the tissue?
Elastic fibers
Gel like or slimy, the major constituents of the amorphous ground substance
Proteoglycans and hyaluronic acid
The glue that holds the fibers and cells together
Glycoproteins
_________ + __________ = ECM
Fibers + ground substance
Where is ECM very abundant in the eye?
- Bruch’s membrane
- sclera
- cornea
- lens
- vitreous humor
What is the most abundant protein in the human body?
Collagen
Structure of collagen
Long, rigid structure in which three polypeptides (a chains) are wound around one another in a rope-like triple helix
What are the three a chains of collagen stabilized by?
Interchain hydrogen bonds
How many types of collage are there?
More than 25, as well as additional proteins that have collagen like domains
What are the groups of collagen
Fibril forming
Network forming
Fibril associated
What type of collagen is in the cornea?
Type I and VIII
What type of collage is in the vitreous body
Type II
What type of collage is in the corneal and vascular endothelium?
Type VIII
Collage is a fibrous porcine composed of ______________
a chains forming triple stranded helix
What is collagen rich in?
Proline and glycine every 3 AA
Collagen contains ____________ and ___________ formed by post translational hydrozxylation of proline and lysin residues
Hydroxyproline and hydroxylysine
What are the enzymes that form hydroxyproline and hydroxylysine in collagen?
Prolyl hydroxylase and lysyl hydroxylase
What do the enzymes prolyl hydroxylase and lysyl hydroxylase require to form hydroxyproline and hydroxylysine?
O2, Fe2+, and ASCO RBI acid (vit C) as reducing equivalents
What is Vitamin C required for in collagen?
As a cofactors for the enzymes involved in hydroxylation of proline and lysin residues in collagen
Lack of proline and lysine hydroxylation lead to what?
Impairment of the interchain H bond formation which prevents the formation of a stable triple helix and affects proper cross linking
What greatly decreases the tensile strength of the assembled collagen fiber in scurvy?
Lack of proline and lysine hydroxylation lead to impairment of the interchain H bond formation which prevents the formation of a stable triple helix and affects proper cross linking
Symptoms of scurvy
- easy bruising
- loose teeth and bleeding gums (1st sign)
- poor wound healing
- poor bone development
Crosslinking of collagen fibers occurs __________
Extracellulary
Crosslinking of collagen occurs by the enzyme
Lysyl oxidase
Crosslinking of collagen happens how?
Oxidative deamination of reactive aldehydes that condense to form cross-linking
What happens when there is a deficiency of copper for crosslinking?
X-linked Menkes disease
What happens when there is a copper overload during crosslinking?
Wilson disease
________ is a defect in any of the synthetic steps of collagen
Collagenopathies
Degradation of collagen
Half life is several years, degraded by collagenases
Menkes syndrome is a mutation in the ________ leading to a lack of ______
- ATP7A gene
- Cu2+
Menkes syndrome is inherited in an _____________ pattern.
X-linked recessive pattern
Menkes syndrome symptoms
Weak muscle tone (hypotonia), sagging facial features, seizures, intellectual disability, and developmental delay. The patients have brittle hair (kinky hair disease)
Wilson’s disease is an autosomal recessive condition due to the mutaiton in the ________ gene leading to _________.
- ATP7B gene
- too much Cu2+
Symptoms of Wilson’s disease in the liver
Vomiting, weakness, fluid build up in the abdomen, swelling of the legs, yellowish skin
Symptoms of Wilson’s disease in the brain
Tremors, muscle stiffness, trouble speaking, personality changes, anxiety, and seeing or hearing things
What can you see in the eye that is indicative of Wilson’s disease?
Kayser-Fleischer Rings
Which type of osteogenesis imperfecta is more severe?
Type II
Type I osteogenesis imperfecta
Less severe, may be mistaken for child abuse
-decreased production of certain forms of collagen
Type II osteogenesis imperfecta
Fatal in uterus or in the neonatal period.
-caused by mutations in the collagen genes, mose common of which are substitutions of an AA with a bulky R group (Gly-X-Y)
Common characteristics of osteogenesis imperfecta
- multiple bone fractures
- skeletal deformities
- blue sclera
- hearing loss
- dental imperfections
Why does the sclera appear blue in osteogenesis imperfecta?
Due to thinning tissue hair allows underlying pigment to show through
Ehlers-Danlos syndrome (EDS)
- defective collagen genes or collagen processing enzymes with multiple mutation types
- severity and symptoms depend on which collagen type is affected
Characteristics of EDS
- hyperextensible skin
- hypermobile joints
- easy bleeding/bruising
- may have blue sclera
- most severe forms have potentially lethal vascular problems due to defective collagen in the arteries
Which diseases can cause blue sclera?
Osteogenesis imperfecta
EDS
Composition of elastic fibers
- an inner core of amorphous elastin
- 10nm microfibrils surrounding the elastin composed of the proline fibrilin
What is the most abundant protein in arteries?
Amorphous elastin
What are elastic fibrils composed of in short?
Elastin and microfibrils (fibrilin)
Elastin structure
Connective tissue protein with rubber like properties, can be stretched to several times their normal length but recoil to their original shape when the stretching force is relaxed
Elastin is an insoluble protein polymer synthesized from a precursor ___________
Tropoelastin
What is the main difference between collagen and elastin
Elastin is rich in proline and lysine but contains SCANT hydroxyproline and hydroxylysine
Production of elastin
Lysyl oxidase modifies lysyl side chains in tropoelastin forming a desmosine cross linking which produces elastin
Extensively interconnected, rubbery network that can stretch and bend in any direction when stressed, giving connective tissue elasticity
Elastin
Cause of marfan syndrome
Mutations in the fibrillin-1 protein
Marfan syndrome is a rare ___________ condition
Dominantly inherited
Apapearance of patients with Marfan syndrome
Tall, with long, spidery fingers, lens displacement, media of large arteries is usually weak.
What do patients with Marfan syndrome usually die of?
Die suddenly in midlife after rupture of their dilated aorta
What disease would you see a dislocated lens?
Marfan syndrome
Large complexes of heteropolysaccharide chains associated with a small amount of protein
Proteoglycans
Protein with a variable but typically small amount of carbohydrate
Glycoproteins
Function of proteoglycans
- produce gel like matrix
- form basis of the body’s ground substance
- serve as flexible support for ECM
- sieve influencing the movement of materials through the ECM
- contributes to the viscous, lubricating properties of mucous secretions
What produces a gel like matrix and forms the basis of the body’s ground substance?
Proteoglycans
What serves as a flexible support for the ECM and acts as a sieve influencing the movement of materials through the ECM?
Proteoglycans
What contributes to the viscous, lubticating properties of mucous secretions
Proteoglycans
Proteoglycan aggregates are composed of
- Proteoglycan monomers
- Hyaluronic acid
- Link protein
What is a proteoglycan monomer made of?
- glycosaminoglycans (GAGS)
- a core protein
what do proteoglycan monomers resemble?
Bottle brush
Long unbranched, heteropolysaccharide chains composed of a repeating disaccharide unit [acidic sugar-amino sugar]n
glycosaminoglycans (GAGS)
How many different types of proteoglycans are there in glysoaminoglycans (GAGS?
6 different types divided according to the monomeric compositions, type of glycosidic linkage and degree an location of sulfate units
Where are glycoaminoglycans (GAG) found?
Always found external to the cytosol: inside an organelle or exterior of the cell
What is linked to a serine residue with >100 monosaccharides/chain extending out from it?
A core protein
How many families of core protein are there?
4
A specific glycosaminoglycan not covalently attached to a core protein
Hyaluronic acid
Anchor point
Small protein that stabilizes the association between the core protein and the hyaluronic acid
Link protein
Large complexes of negatively charges heteropolysaccharide chains
Glycosaminoglycans (GAGs)
Characteristics of glycosaminoglycans
- unbranched
- repeating disaccharide units [acidic sugar-amino sugar]n
Characteristics of the amino sugar of the glycosaminoglycan
- D-glucosamine
- D-galactosmine
The amino group of the glysoaminoglycan is usually _____________
Acetylated
-elimates the + charge
Amino sugars on the glysoaminoglycans can be __________
Sulfate
-enhancing the - charge
Acid sugar of the glycosaminoglycans
- D-glucuronic acid
- L-iduronic acid (C-5) epimer
The acidic sugars of the glysoaminoglycans have a _______ that has a - charge at physiological pH
Carboxyl group
GAGs have a strong (-) charge due to ____________ and __________
Carboxyl groups and sulfate groups
Why are glysoaminoglycans (GAGs) extended in solution, repel each other, and develop mydriatic spheres?
Due to a larger number of negative charges
When GAGs are compressed together, they ‘slip’ past each other…
-have repulsive interactions and release water
Decompression of the GAGs results in
Reestablishment of their extended and hydrated nature
What does the extended and hydrated nature of GAGs contribute to?
- hydraulic absorption and resilience of synovial fluid and vitreous humor of the eye
- lubricating effect of mucous and synovial fluid
What are the classifications of GAG’s divided according to?
- monomeric composition
- type of glycosidic linkages
- degree and location of sulfate units
most abundant GAGs in the body, found in cartilage, tendons, filaments and aorta
Chondroitin 4- and 6-sulfate
Most heterogeneous GAGs, and type I is found in corenas; type II found in loose connective tissue proteoglycan aggregates with chondroitin sulfate.
Keratin sulfate (KS) I and II
What is the only GAG not attached to a core protein?
Hyaluronic acid (hyaluronate)
This is not covalently attached to a protein, and only GAG not limited to animal tissue, but also found in bacteria
Hyaluronic acid (hyaluronte)
What is the only GAG not sulfate?
Hyaluronic acid
This GAG is foundin skin, blood vessels and heart valves
Dermatan sulfate
only GAG that is intracellular and a component of mast cells. Serves as an anticoagulant
Heparin
This GAG is acetylated and there are fewer sulfate groups than other GAGs. It is an extracellular GAG found in BM and as a ubiquitous component of cell surfaces
Heparan sulfate
Which is larger, heparin or heparan sulfate?
Heparan sulfate
Synthesis of the core protein
- translated into the ER lumen by ER associated ribosomes
- trafficked to the golgi where it can be glycosylated by glycosyltranferases to form short carbohydrate linkage region
Synthesis of carbohydrate chain (synthesis of proteoglycans)
-synthesis and elongation by sequential addition of alternating acidic and amino sugars by a family of specific glycosyltranferases
Addition of sulfate groups (synthesis of proteoglycans)
Sulfotransferases transfersulfate groups to specific sites on the growing carbohydrate chain
What are the steps of proteoglycan synthesis
- Synthesis of the core protein
- Synthesis of the carbohydrate chain
- Addition of sulfate groups
A defect in the sulfation of the growing GAG chains results in one of several disorders that affect the proper development and maintenance of the skeletal system
Chondrodystrophy
Characteristics of chondrodystrophy
- autosomal recessive
- dwarfism
Degradation of GAGs
Extracellular GAGs enters into the cell by phagocytosis and end up in the lysosomes
Once the GAG is in the lysosomes for degradation
Hydrologic enzymes degrade the GAGs which require large number of acid hydrolases for complete digestion
Half life of GAGs
Varies
- keratin sulfate > 120 days
- others range from about 3 days to about 10 days
Deficiency of any one of the lysosomal hydrolyses involved in heparin sulfate and/or dermatan sulfate degradation leads to _________________
Mucopolysaccharidoses
Progressive disorders characterized by GAGs accumulating in the lysosomes of various tissues results in oligosaccharides in the urine
Mucopolysaccharidoses
Diagnoses of mucopolysaccharidoses
- the specific mucopolysaccharidoses is determined by identifying the structure present at the non-reducing end of the oligosaccharide
- diagnosis is confirmed by measuring the patients cellualr level of lysosomal hydrolases
Symptoms of mucopolysaccharidoses
- apparently normal at birth, gradually deteriorate, severe cases may result in childhood mortality
- a range of skeletal and extracellular matrix deformities and mental retardation
What are the 4 mucopolysaccharidoses diseases?
- Hurler syndrome
- hunter syndrome
- sanfilippo syndrome
- sly syndrome
Hurler syndrome (MPS 1 H) is a ___________ deficiency
Alpha-L-iduronidase deficiency (degradation of dermatan and heparin sulfate deficiency)
Symptoms of Hurler syndrome
- corneal clouding
- meant all retardation, dwarfing
- coarse facial features
- upper airway obstruction
- deposition in coronary artery leads to ischemia and early death
Treatments for hurler syndrome (MPS 1 H)
- bone marrow or cord blood transplant
- enzyme replacement
What is the most severe form of MPS?
Hurler syndrome
Hunter syndrome (MPS II) is a deficiency of what?
Iduranate sulfatase deficiency (dermatan and heparan sulfate)
What kind of genetic disorder is Hunter syndrome?
X linked
Symptom of hunter syndrome
- NO corneal clouding
- physical deformity
- mental retardation
- coarse facial features
- growth deficiency
Treatments for hunter syndrome
-enzyme replacement therapy
Symptoms of sanfilippo syndrome types A-D (MPS III)
- nervous system disorder
- Neumann retardation
What is Sly syndrome deficient in
Beat-glucuronidase deficient (dermatan sulfate and heparan sulfate deficiency)
What MPS is extremely rare?
Sly syndrome (MPS VII)
Symptoms of sly syndrome
- corneal clouding
- depressed nasal bridge, epicanthic folds
- long philtrum, thin upper lip
- hypertrichosis (abnormal hair growth)
Treatments for Sly syndrome
No approved specific treatments
Which MPS diseases cause corneal clouding?
Hurler syndrome and Sly syndrome
What are the functions of membrane bound glycoproteins
- cell surface recognition by other cels, hormones, and viruses
- cell surface antigenicity (blood group antigens)
- formation of the ECM and mucins of the GI and uritogenital tracts. Biological lubricants
Function of non membrane bound glycoproteins
- almost all globular proteins secreted in the plasma are glycoproteins
- many of the lysosomal proteins are glycoproteins
Where are glycoproteins found
Outer surface of the plasma membrane or inside an organelle. Not in the cytoplasm
Structure of the carbohydrate chain in the glycoproteins oligosaccharide
- relatively short
- do not have serial repeats
- often branched
- may or may not be negatively charges
- highly variable
Examples of how variable the composition of carbohydrates are in glycoproteins
- immunoglobulin IgG has < 4% carbs
- gastric glycoproteins (mucin) has >80% carbs
Structure of the linkage between carbohydrate and protein
-an N- or an O-glycosidic link between the oligosaccharide and the protein
N-glycosidic link of the linkage between the carbohydrate and the protein in the glycoprotein
The sugar chain is attached to the amine group of an asparagine side chain
O-glycosidic link between the carbohydrate and the protein of the glycoproteins
The sugar chain is attached to the hydroxyl group of either a serine or threonine R-group
What kind of linkages do glycoproteins have?
They might contain only one type of glycosidic linkage (N- or 0- linked), or it may have both O- and N- linked
O-linked oligosaccharides (glycoproteins)
- Diverse sugars
- may have one or more of a wide variety of sugars arranged in either a linear or branched pattern (usually branched)
- found on extracellular glycoproteins and membrane glycoproteins
This like of linked oligosaccharide may have one or more of a wide variety of sugars arranged in either a linear or branched pattern
O-linked
This type of linked oligosaccharide can be found on extracellular glycoproteins or membrane glycoproteins
O-linked
What helps provide the ABO blood group determinants?
O-linked oligosaccharides on the surface of RBCs help proved the ABO blood group determinant s
What are the two broad classes of N-linked oligosaccharides
- complex oligosaccharides
- high mannose oligosaccharides
What do both classes of N-linked oligosaccharides contain?
The same core pentasaccharide but the complex oligosaccharides contain a diverse group of additional sugars
Complex oligosacharides additional sugars
- GlcNAc
- Fuc
- NANA
High mannose oligosacharides diverse sugars
Contain primarily mannose
Glycoproteins destined for cellular membranes,m lysosomes, or to be exported from the cell as secretory:
- Synthesized On ribosomes attached to the RER
- N-terminus hydrophobic sequence
- extruded into the ER lumen
- proteins transported via secretory vesicles to golgi which acts as sorting center that gives molecular address labels
Where does the O linkage happen for glycoproteins
Golgi only
Where does N-linkage occur?
In the ER, additional sugars and/or modifications may be added in the golgi
How do soluble glycoproteins get distributed?
In the golgi they are packaged into vesicles that fuse with the cell membrane and release their contents
How do membrane glycoproteins get distributed
Integrated into the ER membrane, pass through the golgi, and are packaged into vesicles for delivery to the cell membrnae
Enzymes destined for the lysosomes
- Nlinked glycoproteins can be phosphorylated at specific mannose residues
- mannose-6-phosphate receptors located in the golgi membrane bind the target phosphorylated glycoproteins, concentrates them into vesicles and traffics them to the lysosomes
What is I cell disease a deficiency of
In the ability to phosphorylate mannose
What does the disability to phosphorylate mannose cause for I-cell disease?
Accumulation of large lysosomal inclusion bodies composed of missing hydrolase substrate
What kind of disease is I-cell disease
Lysosomal storage disease
Symptoms of I cell disease
Skeletal abnormalities, restricted joint movements, coats dysmorphic facial features, severe psychomotor impairment
-death likely prior to 8 years old
Where does degradation of glycoproteins occur?
In the lysosomes
What happens when there is a hydrolase enzyme missing in the lysosomes for degradation of glycoproteins?
Other expenses cannot participate in continued component degradation
-lead to accumulation of partially degraded structures in the lysosomes
Deficiencies in the hydrolase enzymes of the lysosomes are what kind of disorder?
Autosomal recessive
