BIOCHEMISTRY SLIDES OF FIBROUS PROTEINS FROM LLIPPINCOTT

1. FIBROUS PROTEINS
Lecture by Dr Sumera Saghir
MBBS, M. Phil , PHD scholar
Biochemistry

2. FIBROUS
PROTEINS

3. Learning objectives
• At the end of the session
• You will be able to define and describe fibrous
proteins
• Describe the synthesis and types of Collage
proteins
• Collegenopathies
• Elastin protein and diseases due to deficiency of
elastin protein
• Differentiate between globular & Fibrous proteins

4. • Fibrous proteins are highly elongated usually
insoluble polypeptides composed of a single
secondary structure element
• Primary component of skin, tendon, bone,
connective tissues, etc
• Function as structural material mechanically
strong & highly cross linked
• Have protective, connective or supportive
roles

5. • Theses are structural proteins ,these
proteins form long fibres give strength to
structures in cell and body.e.g Keratin,
collagen, silk fibrion
• Sclero proteins

6. • Any of various proteins (as collagen and keratin) that
occur especially in connective and skeletal tissues,
• are usually insoluble in aqueous solvents, and are
resistant to chemical reagents — called also
albuminoid
• Main types of Albuminoids :
• Collagen: Most abundant protein in mammals and is
found in connective tissues such as tendons, ligaments,
skin, and bones
•

7. • Elastin: Elastin is a protein found in elastic tissues
such as skin, blood vessels, and lungs.
• It is responsible for the elasticity and resilience of
these tissues, allowing them to stretch and recoil.
• Keratin: Keratin is a fibrous protein found in
tissues such as hair, nails, and the outer layer of
the skin (epidermis).
• It provides structural support and protection to
these tissues and is highly resistant to mechanical
and chemical damag

8. • Keratin Mechanically durable and un-reactive protein
of vertebrates up to 85% of protein
•
• Present in :
• horns, hair, nails & feathers α-keratins occur in
mammals;
• β-keratins occur in birds and reptiles found in hair and
nails
It is a dimer having two subunits held together by
covalent and non covalent interactions
30 keratin genes expressed in mammals

9. • α -keratins are classified as relatively acidic (Type
I) or basic (Type II)
• Keratins have complex quaternary structures
• (a) keratins are dimers composed of a Type I and
Type II subunit
• (b) many dimers associate to form proto-
filaments
• (c) proto-filaments dimerize to form proto-fibrils
• Micro-fibrils associate into macro-fibrils

10. • α-keratin is rich in Cys residues and disulfide bridges
• The mechanical
• strength of horns,
• nails and skin depends
• upon the content of Cys
• Residues and the number of
• disulfide bridges. Extensive disulfide bridging accounts
for the insolubility and resistance to stretching of
• α-keratins

11. Quaternary structure of Keratin

12. Examples
• The α-keratin helix is a right-handed helix, the
same helix found in many other proteins.
• Collagen

14. Collagen
• Present in all multi-cellular organisms and the
most abundant protein in vertebrates
• Extracellular protein that forms insoluble
fibers of great tensile strength
• Major stress bearing component of connective
tissue – bone, teeth, cartilage, tendon, skin,
etc

16. • Collagen is a glycoprotein
• containing galactose and
• glucose as the
• carbohydrate content.
• -

17. Rich in proline and glycine
TRIPLE –stranded helix
Glycine smallest a.acid – every third position
-Gly-Pro-X ---- or (-Gly-pro-hyp--)
Glycine fits into the restricted spaces where the three
chains of the helix come together
Proline / Hydroxyproline constitute about 1/6
Glycine accounts for 1/3

18. • The glycine residues are part of a repeating
sequence, –Gly–X–Y–
• Where X is frequently proline and
• Y is often hydroxyproline (but can be
hydroxylysine. – Proline or a post-translational
modification of Pro (4-hydroxyproline)
• Smaller amount of the modified amino acids,
• 3-hydroxyproline and 5- hydroxylysine also occur
in collagen

19. • 33% glycine
• 10% proline.
• Most remarkably, collagen contains 4-
hydroxyproline (10%), 3-hydroxyproline(
0.5%), and 5-hydroxylysine (1%), which do
not occur in most other proteins.

20. Quaternary Structure
Collagen is composed of
A repeating
Gly – X – Y sequence the X position is typically
Proline and the Y position is often hydroxyproline
Three collagen polypeptides to wrap around one
another forming a right-handed triple helix.
Gly required at every 3rd position to allow close
packing of subunits

22. • A typical collagen
• molecule --- long, rigid
• structure in which three
• polypeptides(referred to as “α chains”) are
wound around one another in a rope-like triple
helix
• Three separate polypeptides, called chains (not
to be confused with helices), are super-twisted
about each other The super-helical twisting is
right handed in collagen, opposite in sense to the
left-handed helix of the chains.

23. Introduce sharp bends in the
–chains (because R group of proline is part of
a cyclic ring), which helps tight wrapping of
these chains around one another.
• Such tight wrapping enhances strength of the
triple helix

24. • Play an indirect role in permitting
• extremely tight inter winding of the -chains.
• The winding is so compact that there is little space
available towards the interior, only the smallest
amino acid, i.e. glycine, can be accommodated at
that place.

25. • Hydroxylation of proline and lysins
• Collagen contains hydroxyproline (hyp) and
hydroxylysine (hyl), which are not present in most
other proteins. – The hydroxylation is, thus, an
example of post translational modification.
• Hydroxyl group in turn can participate in the formation
of an additional hydrogen bond. Formation of a large
number of hydrogen bonds is thus possible, which
gives enormous collective strength. -

26. • Hydroxyproline is important in stabilizing the
triple-helical structure of collagen
• It maximizes interchain hydrogen bond
formation

27. • Prolyl hydroxylase is
• the enzyme that converts
• proline to 4-hydroxyproline
• requires ascorbic acid
• (vitamin C) for activity;
• Deficiency dietary vitamin
• C leads to scurvy

28. • Scurvy is characterized by skin lesions, blood
vessel fragility, poor wound healing and is
ultimately fatal 4-hydroxyproline is
responsible for stabilizing collagen structure
stabilizing is via hydrogen bonds to 'bridging'
water molecules located between individual
subunits of the collagen fiber

29. • Collagen, a fibrous protein,
• has an elongated, triple-helical
• structure that places many of
• its amino acid side chains on
• the surface of the triple helical molecule.
• The three polypeptide α chains are held together by
hydrogen bonds between the chains
• This allows bond formation between the exposed R-
groups of neighboring collagen monomers, resulting in
their aggregation into long fibers.

30. Triple Helix
• while the triple helix is right-handed Gly at
every third position contributes to tensile
strength of helix

31. Collagen Fibrils
• Several common collagens form distinctively
banded fibrils
• Type I collagens have a diameter of 100-2000 A
• Banding arises from packing of collagen
molecules in the fibril
• hydrophobic interactions
• are the driving force
• for association
• of collagen triple helices
• into a fibril

33. Covalent cross-links
• Strength and insolubility of collagen fibrils is
also due to intra- and intermolecular covalent
cross-links not disulfide bonds as collagen is
nearly devoid of Cys
• Cross-links are between Lys (and His) residues
up to 4 residues can be involved in a single
cross-link

34. • Lysyl oxidase – CU++ containing enzyme –
• oxidatively deaminates some of lysyl and
hydroxylysyl residues
• The reactive aldehydes that result – form
covalent cross linkage – mature collagen fibers
These covalent bonds cross-link the individual
polypeptides Give strength and rigidity.
.

35. Menkes syndrome
• Cu++ is required by lysyl oxidase,
• for covalent cross-links to strengthen collagen
fibers
kinky hair and growth retardation, due to
dietry deficiency of the copper

36. lysyl oxidase is
irreversibly
inhibited by a toxin
from plants in the
genus Lathyrus ,
leading to a
condition known
as lathyrism.

37. Lathyrism
• Lathyrus odoratus is a sweet pea that contains
significant amounts of β-aminopropionitrile
• is an inhibitor of lysyl oxidase and prevents the
cross linking of collagen fibrils Increased fragility
of collagen fibrils leads to abnormalities of bones,
joints and large blood vessels
• Aging increases the cross-linking of collagen
• Meat of older animals????
• Old human beings???

38. • The collagen super-family of proteins includes
more than 25 collagen types
• TYPE 1:
• Contains two chains called α1 and one chain
called α2 (α12 & α2)
• makes up about 90 percent of the collagen in
your body,tendons, skin, bones, cartilage, and
connective tissues.

39. • Type I:
• Collagen degrades, it becomes most apparent in your
skin. You’ll likely start to notice wrinkles, fine lines, and
a loss of elasticity.
• TYPE 2:
• Type II collagen contains three α1 chains
• (α1-3 )
• Type II collagen is found primarily in cartilage. While its
structure is also a triple-helix,

40. • TYPE III
• This type of collagen is often found alongside
Type I.
• It makes up muscles, organs, arteries, and
some connective tissues in the liver, spleen
and blood vessels, and internal organs,
including the uterus.

41. • TYPE IV
• Type IV collagen doesn’t form a fibrous triple-
helix structure like Types I, II, and III. Instead,
it creates a web-like pattern, found in the skin,
liver, kidneys, and other internal organs.

43. In some tissues, collagen is dispersed as
Gel that gives support to the structure, e.g
extracellular matrix or the vitreous humor of the
eye.

44. Collagen of bone occurs as fibers arranged at
an angle to each other so as to resist
mechanical shear from any direction.

45. • on the basis of their functions
• and location in the body

47. Types I, II, and III are the fibrillar collagens
Rope like structure
Characteristic banding patterns
Regular staggered packing of individual
collagen molecule

48. Fibril-forming collagens

49. • Fibers are found in supporting elements of
high tensile strength (for example, tendon and
cornea),
• Type II collagen molecules are restricted to
cartilaginous structures.
• Type III collagen are prevalent in more
distensible tissues, such as blood vessels

50. • Types IV and VII form a three-dimensional
mesh, rather than distinct fibrils. For example,
type IV molecules assemble into a sheet or
meshwork that constitutes a major part of
basement membranes

51. Network-forming collagens

52. • : Types IX and XII bind to the surface of
collagen fibrils, linking these fibrils to one
another and to other components in the
extracellular matrix

53. Precursors:
• Collagen is one of the proteins that functions
outside the cell.

54. • Precursors formed in fibroblasts
• Secreted in extracellular matrix
• Enzymatic modification
• Collagen monomer aggregate

55. • Transcription of Collagen Genes:Location: Nucleus of
fibroblasts
• and other
connective tissue cells.
The process begins with the
transcription of collagen genes
(such as COL1A1, COL1A2)
into messenger RNA (mRNA)
within the nucleus of fibroblasts.
Transcription is mediated by specific transcription factors
that bind to regulatory regions of the collagen genes.

56. • Translation of mRNA into Procollagen Chains:
Location: Rough endoplasmic reticulum (RER) of
fibroblasts.
The mRNA molecules encoding collagen are transported
from the nucleus to the rough endoplasmic reticulum
(RER),
where ribosomes translate them into procollagen
polypeptide chains.
These chains consist of three alpha chains (two alpha1
chains and one alpha2 chain) that form a triple helix
structure.

57. • Hydroxylation of Procollagen Chains:
• Location: Endoplasmic reticulum (ER) of
fibroblasts.
Within the endoplasmic reticulum, specific enzymes
catalyze the hydroxylation of proline and lysine
residues within the procollagen chains. This
hydroxylation is essential for stabilizing the triple
helix structure of procollagen.

58. • Glycosylation of Procollagen Chains:
Location: Endoplasmic reticulum (ER) and Golgi
apparatus of fibroblasts.
The hydroxylated procollagen chains undergo
glycosylation, where sugar molecules are added to
specific amino acid residues. This glycosylation
process occurs in the endoplasmic reticulum and
is further modified in the Golgi apparatus.

59. • Formation of Triple Helix Procollagen:
Location: Endoplasmic reticulum (ER) of fibroblasts.
The three alpha chains of procollagen assemble into a
triple helix structure within the endoplasmic
reticulum, forming procollagen molecules.
• Procollagen Secretion:
Location: Golgi apparatus and extracellular space.
Procollagen molecules are packaged into transport
vesicles in the Golgi apparatus and transported to the
cell membrane. These vesicles fuse with the cell
membrane, releasing procollagen into the
extracellular space.

60. Summary
• Cleavage of Procollagen to Collagen:
Location: Extracellular space.
Once secreted into the extracellular space, procollagen molecules
undergo enzymatic cleavage of their N- and C-terminal
propeptides by procollagen peptidases. This cleavage step
converts procollagen into mature collagen molecules.
• Collagen Assembly and Cross-Linking:
Location: Extracellular space.
Mature collagen molecules assemble into fibrils and fibers, guided
by interactions between their triple helix domains. Cross-linking
between collagen molecules occurs, forming stable covalent
bonds that contribute to the strength and stability of collagen
fibrils.

61. continued

65. • Proteolytic activity of collagenase – part of
metalloproteinase
• Normal collagens are highly stable molecules,
having half-lives as long as several years.
• connective tissue is dynamic and is constantly
being remodeled, in response to growth or
injury of the tissue.

66. For type I collagen, the cleavage site is
specific, generating three-quarter and
one-quarter length fragments.
These fragments are further degraded
by other matrix proteinases into
aminoacids.

67. • Several rare heritable disorders of collagen are known
brittle bone disease can arise from a single point
mutation in collagen of bone hyperextensibility of
joints arises from lessening of cross linking in collagen
of ligaments
• Osteoarthritis and atherosclerotic plaques arise from
disruption of collagen in cartilage Defects in any step in
synthesis
• Ehlers – danlos syndrome (EDS)
• Osteogenesis imperfecta (OI)

68. Epidermolysis Bullosa
• It is a heritable disease in which glycosylation
of collagen is impaired and the skin
characteristically blisters.
• the skin breaks and blisters as a result of
minor trauma. The dystrophic form is due to
mutations in COL7A1, affecting the structure
of type VII collagen..

69. Alports syndrome
• The Alport syndrome (hereditary nephritis) genetic
disorders (both X-linked and autosomal)
• Mutations in several genes encoding type IV
• collagen fibers affecting the basement membranes of
the renal glomeruli, inner ear and eye
• The main presenting sign is hematuria, accompanied
by ocular lesions and hearing loss, and patients may
eventually develop end stage
• renal disease

70. Scurvy
• Affects the structure of collagen.
• a deficiency of ascorbic
• acid (vitamin C)
• not a genetic disease.
• Its major signs are
• bleeding gums, subcutaneous
• hemorrhages, and poor
• wound healing.
• Defective synthesis of collagen
• due to reduced
• activity of the enzymes prolyl and lysyl hydroxylases,
which require ascorbic acid as a cofactor

71. Menkes disease
• Deficiency of copper results in defective
• cross-linking of collagen and elastin by the
copper-dependent enzyme lysyl oxidase

72. Effect of Aging and Disease on
Collagen Metabolism
• Age related change is that the collagen of old
animals and humans have more covalent
• cross links than those of the young. Also the
amount of collagen, relative to the proteins of
parenchymal cells, increases with age.

73. Heterogeneous group of connective tissues disorder
Lysyl hydroxylase or procollagen peptidase
Mutation in a.acid sequence of collagen types 1,3,5
Most common type 3
Mutant collagen not secreted
Type 3 component of arteries
• The vascular form, due to defects in type III collagen, is
the most serious form of EDS because it is associated
with potentially lethal arterial rupture.

74. • The classic form of EDS, caused by defects in type V
collagen, is characterized by skin
• extensibility and fragility and
• joint hypermobility

75. • Brittle bone syndrome ( easily fractured even
without trauma) ,hearing loss , and blue sclerae.
• Heterogeneous group disorder
• Retarded wound healing
• Rotated and twisted spine – humped back
(khyphotic)
• Type 1 -- Osteogenesis imperfecta tarda
• defects In type α 1 and α2 chain

76. the most common form, mild bone
fragility,hearing loss , and blue sclerae.
the most severe form,
is typically lethal in the peri-natal period as
a result of pulmonary complications .
In utero fracture , Pulmonary hyperplasia in utero/neonatal
period Mutation in pro α 1 pro α 2 of type 1
replacement of glycine residue by AA with bulky side chain
• .

77. • Type III is also a severe form. It is
characterized by multiple fractures at birth,
short stature , spinal curvature leading to a
“humped-back” (kyphotic) appearance , and
blue sclerae.

78. ELASTIN

79. • Elastin is an extracellular matrix protein that
lends elasticity and resilience to tissues such
as the arteries, lungs, tendons, skin, and
ligaments, rubber like properties
• Elastic fibers ----Elastic fibers consist mainly of
elastin protein and other associated
molecules, including fibrillin microfibrils.

80. • Lungs , large arteries and elastic ligaments
• Can be stretched to several times their
normal length

81. Structure of elastin
• Amino Acid Composition:
1. Elastin is composed primarily of non-polar
amino acids, particularly glycine, alanine, and
valine, which account for over 90% of its amino
acid residues.
2. Rich in proline and lysine (play crucial roles in
the formation of cross-links within the protein.)
3. little quantity of hydroxyproline and
hydroxylysine

82. • Insoluble protein
• Precursor tropoelastin
• Linear polypeptide ---
• 700 AA

83. • Hydrophobic Domains: Elastin contains
hydrophobic domains rich in glycine and
alanine residues. These hydrophobic regions
facilitate the close packing of elastin
molecules, contributing to the insolubility and
stability of the protein.

84. • Cross-Linking Domains:
• These cross-links, which include lysine-derived
desmosine, are crucial for stabilizing the
elastin network and conferring elasticity to
tissues.

85. • Tropoelastin: The precursor to elastin is
tropoelastin, a soluble monomeric protein
synthesized by fibroblasts and other
connective tissue cells.
• Tropoelastin molecules undergo extensive
post-translational modifications, including
removal of signal peptides and glycosylation,
before being incorporated into elastic fibers.

86. • Fibrillin Microfibrils: Fibrillin microfibrils
provide a scaffold for the deposition and
organization of elastin molecules within elastic
fibers.
• Tropoelastin – secreted in extracellular space
• Interact – specific glycoprotein microfibrils –
fibrilin--- scaffold onto which tropoelastin
deposit

87. • Elastin-Cross Linking: The final step in elastin
assembly involves the cross-linking of
tropoelastin molecules to form mature elastin
fibers. Lysyl side chain – oxidatively
deaminated – lysyl oxidase – allysyl residue
• Three allysyl and one lysyl – desmosine cross
link

89. Role of alhpa-1 antitrypsin in elastin
degradation
• Alpha 1 antitrypsin – protein in blood and
body fluids (antiproteinase)
• Inhibit proteolytic enzymes (proteases or
proteinases )
• Alpha 1 AT inhibit neutrophil elastase –
alveolar walls and other tissues
• Most Alpha 1 AT -- synthesized in liver

91. • Single purine base mutation
• GAG ----- AAG
• Substitution of lysine for glutamic acid at position 342
of protein
• Decrease secretion of alpha 1 AT by liver
• causes the normally monomeric
• AAT to polymerize within the ER of
• hepa tocyte s , resulting in decreased secretion of AAT by
the liver.

92. • Methionine 358 in AAT is required for the binding
• of the inhibitor to its target proteases . Smoking
causes the oxidation and subsequent inactivation
of the methionine , there by rendering the
inhibitor power less to neutralize elastase.
• Smokerswith AAT deficiency,, have a considerably
elevated rate of lung destruction and a poorer
survival rate than nonsmokers.

93. • Deficiency can be reversed
• Weekly I/v administration of alpha 1 anti-
tripsyin

94. Difference between Collagen & elastin

95. Clinical Correlates of Elastin deficency
• Deletions in the elastin gene (have been
• found in approximately 90% of subjects with the
, a developmental
disorder affecting connective tissue and the
central nervous system, supravalvular aortic
stenosis often found in this condition.
• Fragmentation or, alternatively, a decrease of
elastin is found in conditions such as pulmonary
emphysema, cutislaxa, and aging of the skin.

96. • It is a glycoprotein, which is essential for the formation
of elastic fibers found in connective tissue.
• It is secreted into the ECM by fibroblasts and becomes
incorporated into the insoluble microfibrils.
• Microfibrils are fine fiber-like strands 10 to 12 nm in
diameter which provide a scaffold for the deposition
of elastin in the ECM. Fibrillins are large glycoproteins
(about 350 kDa) that are major structural component
of these fibers.

97. Clinical correlates of Fibrilin
• Marfan syndrome is a relatively prevalent
inherited disease affecting connective tissue
• It affects
• eyes (eg, causing dislocation of the
lens,known as ectopia lentis),
• skeletal system (most patientsare tall and
exhibit long digits [arachnodactyly] and
hyperextensibility of the joints)

98. • causing weakness of the aortic media, leading
to dilation of the ascending aorta).
• Mutations in the gene(on chromosome 15)
for fibrillin-1

99. Marfan Syndrome
• Clinical appearance:
long extremities
short trunk
chest is deformed
fingers are long and thin
• Defect in collagen crosslinks
Misalignment of collagen molecules in collagen
fibrils

100. Fibrion protein
• Fibrion is a fibrous protein-based bio materials (
silk, keratin, elastin and resilin) for tissue
regeneration &repair.
• Fibroin is rich in Ala and
• Gly residues, permitting
• a close packing of sheets
• and an interlocking arrangement of R groups
• Silk proteins can be extracted from silk glands or
silkworms cocoons

101. • Silk fibrion
• Silk Fibroin Fibroin, the protein of silk, is
produced
• byinsects and spiders. Its polypeptide chains
are predominantlyin the conformation.

102. • Globular
• Globular protein is
soluble and tends to be
involved in metabolic
functions e.g cellular
messengers, enzymes etc
• The shape of a globular
protein is a sphere ,have a
folded ball like structure.
• Fibrous
• Fibrous proteins are a are
insoluble and that helps
in building up the
structuralelements
• e.g formation of tendons,
connective tissues, and
fibers.
• Fibrous proteins are long
and narrow in shape and
have a helical or sheet
like structure.

103. • Globular
• soluble in water
• example of globular
protein is hemoglobin
• They are made up of
primary, secondary,
tertiary, and sometimes
also quaternary
structures.
• Fibrous
• Insoluble in water
• examples of fibrous
protein are elastin,
collagen, actin, fibrin,
myosin, keratin.
• the shape of elongated
strands like rods and
wires, of polypeptide
chain which results in the
formation of it’s sheet like
structure

104. • Globular
• Have a weak
intermolecular
interaction between
them intermolecular
hydrogen bonding.
• Fibrous
• Fibrous proteins have a
strong intermolecular
interaction between
them.