Lecture 10 - Cartilage Structure And Composition Flashcards
What stabilises collagen?
Covalent cross-links
How is a cross link formed?
Formed by two lysine residues which are joined together to form an aldol cross link
What is ehlers danlos - type 5?
It is a syndrome where collagen should be strengthen but instead you get stretchiness
What is SCAD?
Spontaneous coronary artery dissection - which means that the coronary artery splits as the collagen is ineffective in holding the vessel together and results in a heart attack
What are heterofibrils collagens used in adult articular cartilage?
Type 9 and type 11, type 2 is the main collagen type in adults
What can mutations in collagens 9 and 11 result in?
Chondrodysplasia syndromes
What collagen can be seen in cartilage?
Type 3 - it seems to get more prevalent in oesteroarthitus
What is noticeable in the histology with someone who has osteoarthritis (OA)?
There are fewer cells - the cells are dividing but there are spaces where they are no cells
What makes a proteoglycan?
Protein and glycan (polysaccharide)
Proteoglycans are a special class of …..
Glycoproteins
What are proteoglycans normally low and high in?
Low in proteins and high in polysaccharide chains
What type of specialised polysaccharide chains are attached to proteoglycans?
Glycoaminoglycans (GAG chains) which are joined by their reducing terminal sugar residues to the protein
What do proteoglycans give?
‘Bottle-brush’ confirmation (how it looks)
What is attached to the central protein core of a proteoglycan?
GAG chains - which forms the bottle brush Structure
Are GAGs highly negatively charged or positively charged?
Highly negatively charged with lots of esters attached to
What is an aggrecan?
An aggrecan is a cartilage proteoglycan (all glycoproteins end in can)
Why is cartilage proteoglycan called an aggrecan?
Because it aggregates which means it can form gel like properties
How can aggrecans be measured?
By finding an increase in viscosity
What is the structure of aggrecans?
3 globular domains with a protein core, an N terminal G1, two types of GAGs and keratan sulphate chains (KS) and Chondroitin chains (Cs)
What globular chain is very important in aggregation?
G1 which is also the N terminal
What are the two ways the Cs chains can be arranged?
Regulatory spaced (Gs1) and in clusters (Gs2)
What sulphate chains are shorter, keratan or chondroitin?
Keratan are shorter
What is the structure for keratan?
A repeating disaccharide structure, for every disaccharide you get more negative charge
What is different for the structure of Keratan and the structure for chondroitin?
Chondroitin has a Glucuronic acid (glucosamine) and keratan has galactose (galactosamine)
What is imporant when you stop growing?
Need to stabilise the matrix, stabilise the cartilage so C-6 sulphate is important as well as Keratan
What is different to babies and adult cartilage?
The cartilage in babies need to be remodelled, as babies grow therefore cartilage needs to be broken down or calcified to be converted into bone
What could happen when you damage cartilage?
The body could use the wrong proteoglycans - could used foetal proteoglycans
What happens after every repeating disaccharide in chondroitin cartilage?
Get two negative charges
What specific linkage so GAGs have?
Glycosidic linkage (O)
What does the level of glycosylation depend on?
The age of the tissue
What does aggrecan glycosylation contain?
100 CS chains, 30-60Ks, CS-1 evenly distributed and CS-2 clusters with a MW of 2 million
How many repeating disaccharide units does aggrecan glycosylation have in Cs chains?
40 repeating disaccharides with 80 negative charged per chain
What is the aggrecan glycosylation like Ks chains?
8000Mw, 8-16 repeating chains with 8-16 negative charges over chain
What is the aggrecan protein core like?
G1 - is the N terminal globular region which interacts with another glycosaminoglycan (HYALURONAN)
Is hyaluronan sulphated?
NO
What is the size of the proteoglycan aggregate dependent on?
How long the hyaluronic acid is
What are proteoglycans in the extracellular matrix present as?
Multi molecular aggregates
What do aggregates consist of?
Many proteoglycan monomers bound to a single molecule of hyaluronan by an IONIC interaction
What does the ionic interaction do in proteoglycan aggregates?
It is stabilised by 2 link proteins with MW of 40,000 and 50,000
How large can aggregates be?
Can have a MW weight up to 1million
What is hyaluronan important in?
In developing the hindlimb
HAS =
Hyaluronic acid synthetase (HAS2) - important in developing the hindlimb
What happens if you delete HAS2 genes?
Results in much shorter limbs and the joint is not properly formed
What is the development of the joint and limbs like?
Starts off as cartilage and as the joints develop it gets calcified and becomes bone
What is the structure of link proteins?
Has immunoglobulin like folds - two other globulin domains which are tandem repeats
What is the structure of G1?
It has a similar structure to link proteins, it has N linked sugars which would be linked to asparagine
What can G1 interact with?
Hyaluronic acid, it has one A and two B domains, the B domains are involved in binding to hyaluronic acid, A domains bind to each other binding to the link proteins
How many sugars of hyaluronic acid is important for binding?
It needs 10 sugars to = 5nm
How big are the globular domains?
3x3nm which is big enough to get the 10 sugars of hyaluronic acid
What is involved in maintain hydrophobic amino acid?
Tryptophan and is maintains the globular conformation of G1
What is necessary to get a reaction between the G1 region and reaping unit of hyaluronan?
3-Nacetyl groups
What is the interaction between proteoglycan and hyaluronan like under physiological conditions?
An equilibrium exists between PGS, HA and the complex, equilibrium will shift in favour of the complex group, there is no equilibrium once you add link proteins
What has been found in recent studies to do with HAS2?
On cartilage specific HAS2 knockout mice - in the absence of HAS2 gene expression it resulted in severely abnormal Skeleton and perinatal death - Roughley P.J (2006)
