Class: Fundamentals
Date: August 16, 2011 11:00-12:00
Professor: Detloff
I.
Collagen Chemistry and Biology
Scribe: Frannie Davis
Proof: Nicola Gough
Page 1 of 5
COLLAGEN CHEMISTRY AND BIOLOGY [S1]
a. The collagens are proteins that can form these fibrous structures that are incredibly important in organisms for the
sustenance of the formation of bone, etc. (he actually said etc.)
b. Collagen is the most abundant protein in mammals
i. 25% of your protein mass is collagen based
c. Collagen is a group or class of proteins that form a particular structure.
i. Collagens actually have these repetitive sequences in them
ii. Every third amino acid is a glycine
1. Glycine has the simplest “R” group of all the amino acids.
2. That “R” group is Hydrogen.
3. This is the smallest amino acid.
4. That Hydrogen in the “R” group provides the least steric hindrance; this will become important to
collagen structures.
iii. X and Y are just 2 different amino acids and then every third residue or amino acid (those are
interchangeable by the way) inside a collagen molecule is a glycine.
iv. This allows the formation of these triple helical domains in glycogen that allows these long structures to
form that provides strength and structure to different organs in the body.
v. There are also these non-triple helical domains that interact so that multimolecular aggregates can form.
d. There are many, many things that the collagens do. They are primarily structural elements in extracellular spaces.
II. LOCATIONS OF COLLAGENS (SKIN) [S2]
a. So they are a large component of skin.
III. LOCATIONS OF COLLAGENS (BASEMENT MEMBRANES) [S3]
a. They are present in the basement membranes of tissues.
IV. LOCATIONS OF COLLAGENS (VASCULAR SYSTEM) [S4]
a. They are present in the vascular system giving strength to arteries and veins.
V. LOCATIONS OF COLLAGENS [S5]
a. They ARE the major structural component of bone.
b. They are also a structural component that gives some rigidity to cartilage as well.
c. Tendons, ligaments..
VI. LOCATIONS OF COLLAGENS (TEETH) [S6]
a. And Teeth
VII. LOCATIONS OF COLLAGENS (EYE) [S7]
a. They are present in the eye. Actually the capsule around the lens is made up of collagens and when that is pulled it
can change the focus of the lens.
i. Very important for that.
VIII. POSTERIOR POLYMORPHIS CORNEAL DYSTROPHY [S8]
a. There are mutations in the collagen that you may see in clinical practice.
i. They are fairly rare.
b. This is a mutation in the collagen 8A2 (COL8A2) gene. This individual has dominantly acting, so this is a single copy
of this mutation.
c. You can see here this is a slit lamp and do you see all of that lighter blue junk in the cornea? That is NOT supposed
to be there.
IX. OSTEOGENESIS IMPERFECTA [S9]
a. This is created by mutations in the collagen genes or the loss of a collagen gene.
b. Caused by the mutation in these 2 collagen genes, COL1A1 and COL1A2.
c. These individuals with this, as you might guess by the name, actually have bone problems, but they also have this
unusual feature of having a blue sclera.
i. You can see the blue. This is not supposed to be present in the white of the eye.
X. COLLAGEN TYPES [S10]
a. All of these different properties and the ability to form all these different structures and do all these different
things in the body is due to it having 45 genetically distinct polypeptides that is coded at 45 different genes.
Class: Fundamentals
Date: August 16, 2011 11:00-12:00
Professor: Detloff
b.
c.
Collagen Chemistry and Biology
Scribe: Frannie Davis
Proof: Nicola Gough
Page 2 of 5
They can form 27 different types of collagens.
There are fiber-forming collagens.
i. The most common is type I (one).
ii. And there are type II (two) and type III (three) as well.
iii. Fiber-forming collagens predominate the amount of collagens inside the body. Although the other
collagens are just as important, because genetic mutations in them cause disease.
iv. They undergo this cleavage event. They are coded for in the genome into a polypeptide that is
procollagen, that gets cleaved later to form the actual collagen that we see in these fibrous structures.
v. The fibers are actually constructed of staggered, side to side, parallel associations of the molecules.
vi. Remember, the collagen itself is a triple helix. There are three different polypeptides, these tropocollagen
molecules that wind together to form a triple helix and that is the subunit of the structure of these fibers.
XI. COLLAGEN TYPES, CNTD.[S11]
a. There are other types of collagens that don’t form these structural limits? This is just to show you the diversity of
them.
b. They are usually smaller; they sometimes have these triple helical domains but not all the time.
c. They seldom have the cleavage event that gives procollagen to collagen in the extracellular space of these
structural fibrous collagens.
d. They are sometimes side to side, and anti-parallel associations. They can still aggregate.
XII. COLLAGENS: PRIMARY STRUCTURE [S12]
a. In the primary structure of collagen, as I described earlier, almost every third residue is a glycine.
b. According to the definition, every third residue is a glycine, but there can be mutations that create a gene that
codes for a collagen that does not have a glycine in the 3 position.
i. These are structurally much weaker
ii. In fact, if you look at Osteogenesis Imperfecta (the slide with the blue sclera), the entire loss a collagen
gene, the heterozygous loss of it, can cause a mild form of this Osteogenesis Imperfecta.
iii. But a point mutation that swaps out the glycine for something with a bigger “R” group (which is any other
amino acid) that causes a much more severe form.
1. Probably because the structure is altered. Sometimes having something there that is broken (or
has a mutation in it) is far worse than not having this protein at all.
2. This is a common motif of molecular genetics. You do not want something there that is partially
broken. It is better to not have it at all.
c. About 17% of the collagen protein is proline.
i. Proline is the one weird amino acid that has two connections to the peptide backbone. Its “R” group is
connected twice (forms this little kind of cyclic structure)
d. Hydroxyproline is also there.
i. It is not coded for in the amino acid as it is made. It is prolines that are changed (hydroxylated) later.
e. There is also hydroxylysine which is important because it can form interchain bonds or it can become glycosylated.
This is an extra hydroxy group that is on the lysine.
XIII. COLLAGEN: A TRIPLE HELIX [S13]
a. So tendons, cartilage, bone, teeth the lens capsule: all these things are connective tissues that are formed by
collagen.
b. The basic unit of collagen is a tropocollagen.
i. There are 3 intertwined polypeptide chains.
1. They have about 1000 (1K) residues each.
ii. Molecular weight of 285,000 (285 kdaltons)
iii. They are long and thin ( 300nm long about 1.4 nm diameter)
iv. They have hydroxylysine and hydroxyproline.
1. Both are formed by a vitamin C ( ascorbic acid) dependent reaction (a hydroxylase reaction)
XIV. COLLAGEN- HYDROXYLATION OF PROLINE [S14]
Class: Fundamentals
Date: August 16, 2011 11:00-12:00
Professor: Detloff
a.
Collagen Chemistry and Biology
Scribe: Frannie Davis
Proof: Nicola Gough
Page 3 of 5
This takes place after the initial polypeptide is formed. Proline is in a particular location, and proline is found
throughout the collagens 17% In fact, when you add proline plus hydroxyproline it can get as high as 30% of the
collagen molecule. So it is rivaling glycine which is 33% all the time.
b. You have this reaction, the prolyl hydroxylase in this case it is forming 4 hydroxyproline. You can see here
hydroxyproline being formed on the polypeptide (the purple O). There is a release of carbon dioxide.
c. You need ascorbic acid for this to work. We all know that ascorbic acid is also necessary for the lysylhydroxylase
XV. SCURVY-VITAMIN C DEFICIENCY [S15]
a. So when you don’t have enough vitamin C or a vitamin C deficiency then your collagen gets messed up. Scurvy
creates a problem with collagens because they are not properly hydroxylated.
i. The extra hydroxyl groups help with Hydrogen binding in these triple helical domains that are formed in
the tropocollagen molecule.
b. There are a lot of bone problems that occur and other kind of connective tissue problems, in particular bleeding
that occurs.
c. IF you don’t have the proper collagen in your vascular system that creates this weakening of vascular walls that can
lead to bleeding that occurs in scurvy.
d. Scurvy if not treated by eating citrus fruits or getting vitamin c inside the body is lethal.
e. These red pockets between the teeth, the gingival red triangles, are just one aspect of what happens with scurvy.
XVI. COLLAGEN-A TRIPLE HELIX [S16]
a. 4-hydroxyproline, 3-hydroxyproline, 5-hydroxylysine, and proline: unusual amino acids
XVII.
THE COLLAGEN TRIPLE HELIX [S17]
a. The unusual amino acid makes a single collagen chain unsuitable for creating an alpha-helix or beta chain.
b. Instead a left handed helix is formed, and then that left handed helix intertwines in a right handed way to create
this triple helix structure.
XVIII.
COLLAGEN-A TRIPLE HELIX [S18]
a. Which is shown in both places right here.
b. This is showing what the x-ray refraction data all summarized together for a poly (gly pro pro) molecule would look
like and this is what we think that collagen looks like as well.
XIX. COLLAGEN FIBERS [S19]
a. Collagen fibers are formed form these tropocollagens triple helixes to give you a staggered array of these
tropocollagens.
b. One tropocollagen can interact with another tropocollagen; there are a lot of hydrogen bonds that can occur.
c. They tend to form these clusters of collagen molecules.
XX. COLLAGEN-A TRIPLE HELIX, CNTD [S20]
a. If we look at them under EM, they look like this. This would be in a bone you would see this kind of structure.
b. These gaps you see under electron microscopy (EM) have a very regular pattern and you can measure all of these
and you can actually see that the pattern where there is a gap are probably due to where there are only 4
molecules across rather than 5 ( this would be the gap).
c. These tropocollagen triple helixes here can be the same polypeptide intertwined with itself or a combination of all
the different collagen molecules that give you this ultimate triple helical structure.
d. This regular pattern is supplemented with cross linking between these collagen fibers.
XXI. STRUCTURAL BASIS OF THE COLLAGEN TRIPLE HELIX [S21]
a. The triple helix is probably formed because glycine is in the center. Every third position is facing inward on this
triple helix, and glycine is the only thing that can fit in this third position, because all the other “R” groups are too
big.
b. Proline and hydroxyproline(HyP) also suit the constraints that are needed across the peptide bond, these angles
you learned about earlier, to give this left handed helix inside the right handed triple helix.
c. The interchain H bonds involving HyP stabilize the helix. Without those there would be destabilization of the helix.
You can that by removing ascorbic acid from the diet creating scurvy.
d. Fibers are further strengthened by interchain covalent lysine-lysine and interchain hydroxypyridinium crosslinks.
i. So there are other crosslinking going on.
XXII.THE HOLE REGIONS OF COLLAGEN FIBRILS..[S22]
Class: Fundamentals
Date: August 16, 2011 11:00-12:00
Professor: Detloff
a.
XXIII.
XXIV.
XXV.
XXVI.
XXVII.
XXVIII.
XXIX.
Collagen Chemistry and Biology
Scribe: Frannie Davis
Proof: Nicola Gough
Page 4 of 5
Remember I showed you this “hole” region were the fibrils are staggered in a certain way and it creates this what
looks like a Hole in the EM. In this region there is a lot of modification of the hydroxylysine
i. One of the modifications is the addition of galactose and glucose.
1. This is done in a stepwise pattern and can occur in the gap region.
2. Thought to help with the recruitment of hydroxy appetite, which is Calcium, that is how bones
become mineralized.
LYSYL HYDROXYLATION [S23]
a. This just shows the reaction, and these are a really detailed here.
b. This is galactose that is added on here, this glycosidic linkage.
c. Down here we have glucose being added on to the bottom by a separate enzyme.
d. We will talk about these structures tom.
MINERALIZATION [S24]
a. These kinds of holes in the collagen which are based on how these triple collagen triple helices interact with one
another.
i. These little holes have these disaccharides there. The Hydroxy appetite (which is calcium with phosphate
and a hydroxide ion) and that can form crystals inside that gap regions.
SYNTHESIS-ASSEMBLY OF A COLLAGEN MOLECULE [S25]
a. There are a lot of modifications we have talked about inside this molecule that are post translational.
b. These fibers are extra cellular. They have to be pumped out of the cell
i. When proteins are made to be pumped out of a cell they are made on the RER.
c. The lumen is essentially outside of the cell (it is inside the cell) but anything that is inside lumen can, through the
process of exocytosis, can be pushed outside the cell.
d. While it is being made it is pumped into the ER.
e. This is showing polypeptides being formed.
f. In the ER the enzymes that carry out the glycosylation, hydroxylation, and glucosylations are inside the lumen.
g. The heads of the individual collagen subunits stick together and a coil is formed afterwards (after all the prolines
and lysines become hydroxylated)
h. Then association occurs and the triple helix is formed. The extra little portions on the end do not become part of
the fiber.
i. This is secreted outside the cell.
SPECIFICITY OF CHAIN ASSOCIATION [S26]
a. The C terminus provides specificity to which collagen fibers will stick together.
i. It is not part of the ultimate fiber.
EXTRACELLULAR PROCESSING OF COLLAGEN [S27]
a. Once it is in the extracellular space there are these proteases that cleave off the N and C terminus giving just the
triple helical arrangement.
b. They are laid down in a particular pattern such that this lysyl oxidation can occur and form these covalent bonds
between other triple helices.
c. This regular structure might be partly dictated by how those bonds can form.
i. They can only be formed at certain lysine groups within regular area.
CROSSLINKS IN A FIBER: PHYSICAL STABILITY [S29]
a. This cross linking gives it physical stability
FIBROUS COLLAGEN SUMMARY [S30]
a. This slide summarizes it here
i. You have a fibril. Which the distance across is 5 triple helices. There should be 15 actual independent
polypeptides (3*5).
ii. Hole area-(said same thing as before-hydroxy appetite..)
iii. These fibers are present in tendons and ligament and cartilage
1. When cartilage is damaged it can create a mutation in a collagen molecule and it can become
bone like after injury
iv. Repeats again (left handed and right handed, modifications [gly every 3])
Class: Fundamentals
Date: August 16, 2011 11:00-12:00
Professor: Detloff
XXX.
XXXI.
Collagen Chemistry and Biology
Scribe: Frannie Davis
Proof: Nicola Gough
Page 5 of 5
v. It can have sugar residues added to those lysines and crosslinking can occur between triple helical
segments that gives the fiber the very strong structure.
INDUSTRIAL AND CLINICAL USES OF COLLAGEN [S31]
a. Gelatin is hydrolyzed and denatured collagen.
i. It is used for many things:
1. Coating pill capsules cases
2. Foods
b. Native collagen:
i. Can be used to puff up lips and fill wrinkles in faces.
1. The injections of collagen can produce an immune reaction which can lead to tissue rejection in a
way
ii. Used in surgical dressing
iii. Some implants.
iv. Tissue engineering- if you want to grow bone like structures collagen is added into the mix of what is
injected.
CROSSLINKING [S32 &S33]
a. Do NOT have to know these last two slides.
[end 30:28 mins]