Proteoglycans Flashcards
(30 cards)
What is a proteoglycan?
Proteoglycans are poly anions with many negative charges . They are hydrated with water and bound Na+ causing a swellign pressure that can withstand compression.
What is a proteoglycan composed of?
Proteoglycans (PG’s) are composed of a central core protein and repeating disaccharide, glycosaminoglycan (GAG) made of an N-amino sugar and an acid sugar.
What do proteoglycans do?
They act as shock absorbers (cartliage) and jount lubricators (synovial fluid)
How do proteoglycans Interact with one another?
Some proteoglycans form large aggregates
How do proteoglycans funcion in hydrated gels?
There are many polyanions attached to the core protein molecule that hae many negative charges. these polyanions are hydrated with water and bound Na+ causing a swelling pressure that can withstand compression.
Similiar to the brush you use to clean out test tubes.
Describe the volume of Glycoseaminoglycans (GAG’s)
Glycosaminoglycans (GAG’s) have a very high volume relative to their mass because they are highly hydrated molecules. Their rigid nature and hydration make them very efficent shock absorbers.
How do proteoglycans interact with other molecules?
Do proteoglycans interact with molecules in the extracellular matrix? If so what type of interactions do they take part in?
What is an example of a protein that interacts with polyoglycans?
Proteoglycans interact with other molecules largely by ionic interactions.
Yes, Proteoglycans interact with molecules in the intracellular matrix via ionic interactions of the polyionic GAG chains with positively charged regions of extracellular proteins.
Collagen
What are some common features of osteoarthritis?
Where does it occure?
What is the result?
Cartelage degeneration in the joints of the hip, knee, and hand.
Spinal degeneration can occure in the intervertebral discs and facet joints
Results in increased friction and mechanical stress, loss of joint mobility and PAIN
Where are proteoglycans synthesized?
Proteoglycan core proteins are synthesized in the RER of **Chondrocytes. **
They are then modified in the golgi and exported from the cell.
What is a glycosaminoglycan?
What are the functional units that make up this molecule?
How are they linked to the core protein?
A repeatind disaccharide which forms the “glycan” of the proteoglycan molecule. They are composed of amino sugars (which can be sulfinated or acetylated) and acid sugars which contain carboxyllic acid.
GAG’s are linked to the core protein via O-Glycosidic linkages to serine residues in the protein backbone
How are different proteoglycans identified?
What are two commo types?
By the composition of the glycosaminoglycan chains linked to the central molecule through O-Glycosidic Linkages
Keratin sulfate = keratin
Chondroitin sulfate is another common GAG
Hyaluronate makes hylane cartlidge
Is each glycoaminoglycan a pure repeating structure?
Yes
Identify the acid sugar and the amino sugar
Acid sugar is in the top left, COO- and the amino sugar is in the bottom right.
Describe the common features of Hyaluronate
Pronunciation: (hy·al·uro·nate)
This exists as a free GAG, not covalently attached to protein like in proteoglycan. Not sulfated. Found in cartilage, synovial fluid, vitreous humor.
What are the common features of Chondroitin Sulfate, Dermatan Sulfate, Heparin and Heparan Sulfate
GAGs are covalently attached to proteins through serine and a link trisaccharide, xyl-gal-gal-. They are sulfated. Found in many connective tissues and cell surfaces.
How are glycosaminoglycans linked to the peptide backbone?
What is the defining characteristic of the serine recognition sequence?
Serine Link Trisaccharides Link the glycosaminoglycans to the protein backbone through O-Glycosylation to the serine recognition sequence in the protein backbone.
The Serine recognition sequence is
ASP/GLU-X-SER-GLY
In linking the GAG’s to the protein backbone what follows the trisaccharide link sequence?
The repeating disaccharides that form the glycosaminoglycan follow the trisaccharide link sequence.
What are variations in size of the the proteoglycans?
What is a very large proteoglycan mentioned?
What is a very small proteoglycan mentioned?
Proteoglycans can range in size depending on the number of glycosaminoglycan side chains and size of the protein backbone.
Aggrecan is a very large proteoglycan
Decorin is a very small proteoglycan
What is the function of the proteoglycan Aggrecan? What structures does it form aggregates with?
Aggrecan is a large proteoglycan that can aggregate with link proteins and hyaluronate to form very large aggregates. Forms Cartlidage
How does fibroblast growth factor interact with proteoglycans?
What process in the cell is fibroblast grown factor useful for?
Proteoglycans can store fibroblast growth factor (FGF) in the glycosaminoglycan side chains to make it readily available when needed by the cell.
These growth factors can be released when the cell undergoes trauma the begin the healing process.
**They control the availability of the growth factor to the cell.
Do cell surface proteoglycans and extracellular matrix proteoglycans interact?
Yes, cell surface and extracellular proteoglycans aid in the interactions with cell surface adhesive proteins like integrin and fibronectin.
What function other than cartlidge, shock absorption, and growth factors do proteoglycans serve?
They adhere cells to other molecules like velcro
THIS IS A WEAK INTERACTION
Can proteoglycans function as cell receptors?
Yes, they can function as multivalent cell surface receptors ,and integral membrane receptors
How are proteoglycans recycled?
What do defects in recycling proteoglycans result in?
The core protein can be internalized and recycled. However, the glycosaminoglycan sidechains are degraded.
Defects in the recycling of proteoglycans and mucolipids on the cell surface leads to mucopolysaccharideridoses
