Transcript 47_Biochemistry of Connective Tissue

Why study tissue proteins?
 To understand normal body functions .
 In development
 In inflammatory states
 Aging process.
 To identify the cause of various genetic and metabolic disorders related
to tissue proteins
 In the spread of cancer cells.
 Several diseases (eg: Osteogenesis imperfecta and a number of
types of the Ehlers-Danlos syndrome) are due to genetic
disturbances of the synthesis of collagen.
 Components of proteoglycans are affected in the group of genetic
disorders known as the mucopolysaccharidoses.
 To use and apply them in the medical, industrial, commercial fields.
 In food products, cosmetic surgery.
 The gelatin used in food and industry is derived from the partial
hydrolysis of collagen.
Present in all organs
(50 % of body weight)
•skin,
•adipose tissue,
•bones,
•teeth,
•fascia,
•cartilages,
•stroma of
parenchymal inner
organs,
•walls of vessels.
THE STRUCTURE OF CONNECTIVE TISSUE
Cells
Fibers
Extracellular
matrix
Cells
•Fibroblasts
•chondroblasts
Fibers
•collagen
•elastin
Extracellular matrix
•fibroblasts
carbohydrate-protein complexes proteoglycans.
Carbohydrate complexes of
proteoglycans –
heteropolysaccharides
glycosaminoglycans
(mucopolysaccharides).
chondroblasts
The Extracellular Matrix
 The space outside the cells of a tissue is filled with a composite material
called extracellular matrix(ECM).
 This ECM is also known as the connective tissue. It is composed of a) Gel with interstitial fluid.
b) 3 major classes of biomolecules:
 Structural proteins: collagen, elastin and Keratin (epidermal tissues)
 Specialized proteins: e.g. fibrillin, fibronectin, and laminin.
 Proteoglycans(Mucoproteins) : Conjugated proteins consisting of
 Protein + Carbohydrate(5%-95%)
 Carbohydrate part is in the form of Glycosaminoglycans [GAGs].
 Thus, the extracellular matrix (ECM) is a complex structural entity
surrounding and supporting cells that are found within mammalian tissues.
The Extra cellular matrix
PROTEINS OF
CONNECTIVE TISSUE
Collagen
 Most abundant insoluble fibrous protein in
the connective tissue of mammals.
 Makes up about 25% to 35% of the
whole-body protein content.
 Scleroprotein secreted from the cells
called fibroblasts.
 In greek ‘kolla’ means ‘glue’.Collagen is
also called as glue-producer.
 Distribution of collagen varies in different
tissues.
 Also found in mucous membranes,
nerves, blood vessels, and organs.
Collagen fibers in
muscle tendons
Functions Of Collagen
 It imparts strength, support, shape
and elasicity to the tissues.
 It accounts for 6% of the weight
of strong, tendinous muscles
 It provides flexibility, support, and
movement to cartilage.
 It encases and protects delicate
organs like kidneys and spleen.
 It fills the sclera of the eye in
crystalline form.
 Teeth (dentin) are made by adding
mineral crystals to collagen.
 Collagen contributes to proper
alignment
of
cells
for
cell
proliferation and differentiation.
 When exposed in damaged blood
vessels,
it
initiates
thrombus
formation
Types Of Collagen
 In humans, there are at least 19
distinct types of collagen made up
of 30 distinct polypeptide chains
(each encoded by a separate
gene).
 They are subdivided into a number
of classes based primarily on the
structures they form
 However, 90% of the collagen in
the body are of type I, II, III, and
IV.
 These types determine the physical
properties of specific tissues and
perform their specialized function.
Collagen
•It serves to hold together the cells in the
tissues.
•It is the major fibrous element of tissues like
bone, teeth, tendons, cartilage and blood
vessels.
•When a solution of collagen is boiled, the
viscosity of the solution decreases, which
indicates that the native rod like structure is
altered and a protein, with random coil structure
results. It is then called gelatin.
Structure of Collagen
•There are 6 types of collagen,
out of which
type I is the most abundant
form;
it contains 2 chains of alpha-1
and one chain of alpha-2.
•Each polypeptide chain of
collagen has about 1000 amino
acid residues.
•The amino acid composition of
collagen is quite unique.
Structure of Collagen
Consists of three
polypeptide chains
having the left spiral
shape
Three left coiled
chains are again
coiled together to
form the right spiral
bunch
1 chain contains about
1000 amino acids
33 % - glycine
21 % – proline and
oxiproline
11 %– alanine
35 % – all other amino
acids
oxilysine
Oxiproline and oxilysine
are specific only for
connective tissue
Oxiproline
Structure of collagen fibers
Collagen – complex
protein, glycoprotein
Carbohydrates
(monosaccharide
galactose and
disaccharide
galactosylglucose) bind
by glycosidic bonds to
the residues of oxilysine
of polipeptide chain
Reaction of aldoll
condensation
Biosynthesis of Collagen
 Collagen synthesis occurs in the fibroblasts, osteoblasts in bone,
chondroblasts in cartilage and odontoblasts in teeth.
 First synthesized in precursor form of preprocollagen polypeptide chain
in the ribosomes during translation
 The leader sequence of amino acids[signal peptide] in the
preprocollagen directs it to enter the lumen of E.R
 In the lumen of E.R, the Signal peptide is cleaved to form procollagen.
 The proline and lysine amino acids in the procollagen chain undergo
hydroxylation and glycosylation known as post translational
modifications.
 Disulfide bonds are formed between three procollagen chains which
twist around each other to form a triple helix molecule.This step is called
registration.
 This Procollagen molecule is secreted into the extracellular matrix from
the golgi compartment of the E.R.
 Here, the procollagen aminoproteinase and carboxy proteinase
enzymes remove extra terminal amino acids from the procollagen
molecule to form collagen .
 The collagen molecules assemble into fibrils and inturn fibers being stabilized
by the covalent cross-links.
Biosynthesis of
collagen from
Preprocollagen
Synthesis Of Collagen
Abnormalities associated with collagen
 Collagen-related diseases arise from
 genetic defects
 nutritional deficiencies
 They affect the biosynthesis, assembly, postranslational modification, secretion, or
other processes involved in normal collagen production.
 These include :
 Ehler Danlos syndrome
 Alport syndrome
 Epidermolysis bullosa
 Osteogenesis Imperfecta
 Chondrodysplasias [affects cartilage]
 Scurvy
 Osteolathyrism
Ehler Danlos Syndrome
 Ehlers-Danlos Syndrome is a group of inherited connective tissue disorders.
 CAUSE
 abnormalities in the synthesis and metabolism of collagen
 Mutations in the collagen genes: COL1A1, COL1A2, COL3A1, COL5A1, COL5A2
 a deficiency of enzyme lysyl hydroxylase.
 A deficiency of procollagenN-proteinase, causing formation of abnormal thin,
irregular collagen fibrils
 EFFECT
 Mutations alter the structure, production, or
processing of collagen or proteins that
interact with collagen
 WeakenS connective tissue in the skin, bones,
blood vessels, and organs causing Skin hyperextensibility
 Joint dislocations
 Tissue fragility
 Poor wound healing.
Ehler-Danlos
Syndrome
•Hyperextensibility of
skin
•Hypermobility
joints
of
Alport Syndrome
Alport syndrome affecting eyes
 Alport syndrome is a genetic disorder
characterized
by
glomerulonephritis,
endstage kidney disease, and hearing loss.
 It also affects the eyes.
 The presence of blood in the urine
[hematuria] is almost always found in
this condition.
 CAUSE
 Mutations in COL4A3,COL4A4,COL4A5
collagen biosynthesis genes.
 These prevent the production or
assembly of the type IV collagen
network in the basement membranes.
 kidneys are scarred and unable to filter
waste products resulting in hematuria
and renal disease.
Epidermolysis Bullosa
•
Epidermolysis bullosa refers to a group of
inherited disorders that involve the formation of
blisters following trivial trauma.
•
CAUSE
 mutations in COL7A1, affecting the
structure of type VII collagen.
 Type VII collagen forms delicate fibrils that
anchor the basal lamina to collagen fibrils in
the dermis.
 These anchoring fibrils are reduced in this
form of the disease, causing friction and
blistering.
EFFECT
 Blistering and painful sores like third degree
burns
•
Blister
formation
Osteogenesis Imperfecta
 Osteogenesis imperfecta or Brittle Bone
Disease is a genetic bone disorder due to
decrease dcollagen formation.
 CAUSE
 Mutations in the COL1A1 andCOL1A2
genes coding for procollagen chains.
 Replacement of glycine by another
bulkier amino acid resulting in decreased
collagen or improper procollagen
structure forming abnormal fibers.
 Mutations also cause ‘procollagen
suicide ‘
 All these cause brittleness.
 EFFECT
 Thin,t ransclucent, blue scleras.
 Affected infants may be born with
multiple fractures and not survive.
 weak muscles, brittle teeth, a curved
spine and hearing loss.
Chondrodysplasias
 Chondrodysplasias are a mixed
group of hereditary disorders
affecting cartilage.
 One example is Stickler
syndrome,
manifested
by
degeneration of joint cartilage
and of the vitreous body of the
eye.
 CAUSE
 Mutations in the COL2A1
gene, leading to abnormal
forms of type II collagen.
 EFFECT
 shortlimbed dwarfism
 skeletal deformities.
Osteolathyrism
 Osteolathyrism is a collagen cross-linking
deficiency caused
by dietary overreliance on the seeds of Lathyrus sativus
(kesari dal) in some parts of India.
 CAUSE
 Osteolathyrogenic compounds like Betaaminopropionitrile(BAPN) and Betaoxalyl aminoalanine [BOAA] found in
Kesari dhal inhibit enzyme lysyl oxidase
required for the formation of cross links
in the triple helices
 EFFECT
 weakness and fragility of skin, bones,
and blood vessels
 Paralysis of the lower extremities
associated with neurolathyrism
Scurvy
 Scurvy is a disease due to deficiency of
vitamin C
 It is not a genetic disease.
 It is related to improper collagen
formation
 CAUSE
 Vitamin C [ascorbic acid ]is
required as a cofactor
for
hydroxylase enzymes during the
hydroxylation of proline and lysine
in the synthesis of collagen.
 Deficiency
causes
impaired
collagen
synthesis
due
to
deficiency of hydroxylases.
 EFFECT
 Bleeding of gums
 Poor wound healing
 Subcutaneous hemorrhages
Uses Of Collagen
 Industrial Uses
 Collagen is used as temporary thermoplastic glues
in musical instruments like violin and guitar .
 Recently used as a fertilizer
 Gelatin derived from the partial hydrolysis of
collagen is used in food products like desserts,
jellies.
 It is also used in pharmaceutical, cosmetic, and
photography industries.
 Medical uses
 Mild benefit to rheumatoid arthritis patients.
 Keeps the valvular leaflets of heart in shape.
 Helps in the deposition of calcium during aging.
 Used in cosmetic surgery, for burn patients for
reconstruction of bone and a wide variety of
dental, orthopedic and surgical purposes.
 Main ingredient of cosmetic makeup.
 Human collagen is used for immunosuppression
during transplantation.
Elastin
The main constituent of
elastic fibers in
ligaments, walls of large
arteries, lungs.
Molecule contains about
800 amino acid residues
Has globular shape.
Is joined into the fibrous
cords.
Contains a lot of glycine,
alanine, proline, valine
There are no oxilysine
and cysteine
Residues of lisine form
the cross covalent bonds
The net structure is
formed which can strech
two and more times.
PROTEOGLYCANS
Proteoglycans – the main extracellular matrix of
connective tissue. Consist of protein part +
polisaccharide chains
Molecular weight – tens millions.
Polisaccharides - glycosaminoglycans (acidic
mucopolisaccharides) are built from the large
amount of identical disaccharide units.
Disaccharide – aminosugar N-acetylglucosamin or
N-acetylgalactosamin + uronic acid (glucuronic or
iduronic) + sulfate (sometime).
Hyaluronic acid
•Is contained in synovial fluid (lubricant in joints),
vitreous substance of eye
•In rheumatic diseases and arthritis hyaluronic acid
is depolimerized and the viscosity of synovial fluid
is decreased
•Forms the viscous solutions
•Retains water
Heparin
•Is synthesized by tissue basofils
•During degranulation is ejected into the
extracellular matrix
•Participates in the regulation of blood
coagulation.
•Increases the release of enzyme lipoprotein
lipase into blood plasma
Keratins
•Keratine are fibrous proteins present in hair,
skin an nail, horn, hoof, etc.
•They mainly have the alpha helical structure.
•Each fibril has 3 polypeptide chains and each
bundle has about 10-12 fibrils.
• The matrix has cysteine-rich polypeptide chains
which are held together by disulfide bonds.
•The more the number of disulfide bonds, the
harder the keratin is.