Collagen, Biochemistry, SMIMER Subscribe to my youtube channel for such great contents www.youtube.com/c/AwesomeBiochemistry

1. Collagen
DR. KALPESHKUMAR NAKARANI
TUTOR CUM RESIDENT (S.Y.)
SMIMER, SURAT

2. Learning Objectives
• Identify the primary constituents of collagen fibrils and
recognize hierarchal organization (Bloom’s Cognition
Level 1, Remember)
• Predict the phenotypic outcome on a cell, tissue, and
organism caused by a change in the structure of
collagen (Bloom’s Cognition Level 2, Understand)
• Hypothesize the mechanism of a collagen related
disorder (Bloom’s Cognition Level 6, Create)

3. Collagen
• Major component of most connective tissue
• ~25% of the proteins of mammals
• In humans
28 Distinct types of
Collagen
30 Distinct types of
Polypeptide chains
Made up of
Each encoded by
separate gene

4. Types of Collagen
Type Location Type Location
I Skin, Bone, Tendon (Non cartilage) XV Associated with collagens close to basement membranes
II Cartilage, Vitreous humor XVI Many tissues
III Extensible conn. Tissue (skin, lung,
vascular system viz. Artery)
XVII Epithelia, Skin hemidesmosomes
IV Basement membrane XVIII Close structural homologue of XV
V Along with Type-I XIX Rare, Rhabdomyosarcoma
VI Muscle XX Corneal epithelium
VII Dermal epidermal junction XXI Many Tissues
VIII Endothelium XXII Tissue junctions
IX Along with type II XXIII Limited in tissues, mainly transmembrane and shed
forms
X Hypertrophic cartilage XXIV Developing cornea, Bone
XI Along with type II XXV Brain
XII Along with type I XXVI Testis, Ovary
XIII NM Junction & Skin XXVII Embryonic Cartilage
XIV Along with type I XXVIII BM Around Schwann cells

5. Noncollagen ‘Collagens’
• Not classified as collagen but have collagen like domains in
structure
• e.g. C1q
• SPA, SPD (Pulmonary surfactant protein)
• All Collagen types have a triple helical structure
– It can be entire molecule or only a fraction of molecule

6. Mature collagen (Type-I)
• The entire molecule is triple helical
• ~1000 AA
• Each polypeptide subunit (α chain, not α
helix) is twisted into a left-handed poly-
proline helix & 3 residues per turn.
• 3 of these α chains are then wound into a
PARALLEL RIGHT HANDED
SUPERHELIX, forming a rod like molecule
(1.4 x 300 nm) • 3 Left handed
Helices form a right
handed super helix.

7. • The repeating structure, represented as (Gly-X-Y)n is an absolute
requirement for the formation of triple helix.
• X = mostly Proline
• Y = Mostly hydroxyl-proline / Sometimes Hydroxy-Lysine
– Hydroxyl derivatives on Y positions because of specificity of prolyl/lysyl
hydroxylase

8. Why glycine residue at every 3rd
position?
• Glycine is the only AA small enough to be accommodated in the
limited space available in central core of triple helix.

9. X & Y Positions
• Proline/ Hydroxyproline confer rigidity on collagen molecule
• Hydroxyproline & Hydroxylysine are result of post translational
modification
Can be further modified by addition of
• Galactose
• Galactosyl-Glucose
Through O-Glycosidic linkage
(Unique glycosylation site of collagen)

10. Staggering of α chains
• 3 polypeptide chains are
staggered so that Gly,X
& Y residues from the 3
polypeptide chains
occurs at similar level
• And so –NH of ‘Gly’
makes strong H-bond
with –CO of an ‘X(Pro)’
of neighbour chain

11. Gly
X
Y
Gly
X
Y
Gly
X
X
Y
Gly
X
Y
Gly
X
Y Gly
Y
Gly
X
Y
Gly
X
Y

12. “Quarter Staggered”
alignment
• Collagen types (only rod like
fibers) are assembled by
lateral association of these
triple helical units into fibrils
(10-300 nm diameter) in a
‘Quarter staggered’
alignment
• Means, each triple helix is
displaced longitudinally from
its neighbour by slightly less
than 1/4th of its length.

13. Fibril
Many fibrils associates into thicker
FIBER (1-20μm in diameter)
• In some tissues (like tendons)
fibers associates into even larger
bundles, with diameter of 500 μm
Power in Numbers!
Fiber = Strength
Fibril = Weak

14. Covalent cross links provide extra
stabilization (Voet & Voet)
Histidino-dehydro-hydroxyl-mero-desmosine

15. Covalent cross links provide extra
stabilization (Lehninger)
The increasingly rigid and
brittle character of aging
connective tissue results from
accumulated covalent
crosslinks in collagen fibrils.

16. Strength – Triple helix provides tensile strength
Scaffold – Provides organization and structure for the ECM
Without it, what would happen?
 Loss of cell-cell communication
 Cell migration
 Loss of cell shape

17. Collagen – According to macro structure
Collagen
Fibril Forming (1,2,3,5,11,24,27)
Network like (4,8,10)  in BM
Anchoring Fibrils (7)
Multiplexins (15,18)  Multiple triple helix domains with
interruptions
Beaded Filaments (6,26,28)
Transmembrane (13,17,23,25)  Have short intracellular
N-terminal domain
FACITs (9,12,14,16,19,20,21,22)  Fibril Associated
Collagen with Interrupted Triple helices

18. Some collagen types do not form fibrils
• They are characterized by interruptions of the
triple helix with stretches of protein lacking
(Gly-X-Y) repeat sequence
• It results in areas of globular structure
interspersed in triple helical structure

19. Collagen Biosynthesis

20. Genetics of Collagen
• > 30 genes encodes the collagens
Collagen
Heterotrimeric
(Pro-α chains different)
Homotrimeric
(3 identical Pro-α chains)
e.g. Type I Collagen
2 Pro- α1 (I) + 1 Pro- α2 (I)
e.g. Type II Collagen
3 Pro- α1 (II)
Gene Nomenclature:
COL1A2
Gen Prefix
Type of collagen
Type of Chain

21. Gene Nomenclature:
COL1A2
Gen Prefix
Type of collagen
Type of Chain
e.g.
COL1A1  Pro- α1 (I)
COL2A1  Pro- α1 (II)

22. Collagen related disorders

23. Osteogenesis imperfect
(Brittle bone disease)
• C/F
– Abnormally fragile bones
– Blue sclera (Thin & translucent cornea)
• Types (I to VIII) – 8 types
– Type I to IV
 mutation in COL1A1 &/Or COL1A2
 > 100 types of mutations documented
 M.C. mutation is replacement of glycine by another bulky AA
– Types (V to VIII)
 due to mutations in genes encoding for proteins involved in bone
mineralization (Not collagen)

24. • When one abnormal chain is present, it may
interact with two other normal chains BUT
Folding may be prevented
• This leads to enzymatic degradation of all of the
chains.
• This is called “Procollagen Suicide”
• This is an example of a “Dominant negative
mutation”, a result often seen when a protein
consist of multiple different subunits

25. Chondrodysplasia
• Affects cartilage
• C/F:
– Short limb dwarfism
– Numerous skeletal deformities
Chondrodysplasia
Stichler Syndrome
• Mutation  COL2A1 gene
• Abnormal Collagen II
• C/F:
• Degeneration of joint
cartilage & vitreous
body of eye
Achondroplasia
• Mutation  FGFR3 gene
(Chr-4)
• Not a collagen disorder

26. Ehlers-Danlos Syndrome
(Cutis Hyperplastica)
• C/F:
– Hyper extensibility of skin
– Abnormal tissue fragility
– Increased joint mobility
– C/F are variable due to underlying extensive genetic heterogeneity.
• Defect:
– Collagen I/ Collagen III/ Collagen V/ Lysyl Hydroxylase/ Procollagen
N-Proteinase
– Procollagen N-Proteinase = ADAMTS2 = ADAM Metallopeptidase
with thrombospondin type 1 motif

27. • Villefranche Classification of EDS
Type Defect
Hypermobility
Common
Collagen III
Vascular Collagen III Most serious (d/t rupture of arteries/Intestine)
Classical Collagen I & V
Arthrochalasis
Very Rare
Collagen I
Kyphoscoliosis Lysyl Hydroxylase Progressive scoliosis & tendency to ocular
rupture
Dermatosparaxis ADAMTS2
(Procollagen N-Proteinase)
Marked fragile skin

28. Alport Syndrome
(Hereditary Nephritis)
• Defect: Type IV collagen (BM), Also in eye & inner ear)
• C/F:
– Hematuria (ESRD)
– Ocular lesion
– Hearing loss

29. Epidermolysis Bullosa
• Defect: COL7A1 Gene (Collagen type VII)
– Collagen VII is anchoring fibrils that anchor the basal lamina to collagen
fibrils in dermis.
• C/F:
– Skin blisters & breaks due to minor trauma
• Note:
– Epidermolysis bullosa simplex is due to mutation in Keratin 5

30. Scurvy
• Not a genetic disease
• Due to decreased activity of prolyl & Lysyl hydroxylase

31. Menkes disease
• Copper deficiency  ↓ activity of Lysylhydroxylase  defective
cross linking of collagen & elastin
• Note:
• Other Cu containing enzymes
– Lysyl oxidase
– Cytochrome oxidase
– Dopamine hydroxylase
– SOD
– Tyrosinase

32. Lathyrism
• Regular ingestion of seeds of the sweet pea Lathyrus odoratus
• It contains β-amino propionitrile  it inactivates lysyl oxidase
• C/F:
– Severe abnormalities of bones, joints & large blood vessels

33. Thank You