Download Connective tissue

Seema Zargar
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Most diverse and abundant tissue
Main classes
◦ Connective tissue proper
◦ Cartilage
◦ Bone tissue
◦ Blood
Characteristics
◦ Mesenchyme as their common tissue of
origin
(mesenchyme
derived
from
mesoderm)
◦ Varying degrees of vascularity
◦ Nonliving extracellular matrix, consisting of
ground substance and fibers
◦ Cells are not as abundant nor as tightly
packed together as in epithelium
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Enclose organs as a capsule and separate
organs into layers. Areolar
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Connect tissues to one another. Tendons and
ligaments.
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Support and movement. Bones.
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Storage. Fat
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Insulation. Fat.
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Transport. Blood.
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Protection. Bone, cells of the immune system.
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Ground substance – unstructured material that
fills the space between cells
Fibers – collagen, elastic, or reticular
Cells – fibroblasts, chondroblasts, osteoblasts,
hematopoietic stem cells, and others.
Collagen is the main protein of connective tissue
in animals and the most abundant protein in
mammals, making up about 25% of the total
protein content.
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Connective tissue can be classified into three
categories:
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proper,
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embryonic,
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specialized
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Embryonic: Is further divided into
mesenchyme and mucoid.
Specialized: Is further divided into bone,
cartilage and blood.
Connective tissue proper: Is further divided
into elastic tissue, reticular tissue, adipose
tissue, areolar (loose tissue) and dense tissue.
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Collagen is rich in proline and glycine, both of which
are important in the formation of the triple-stranded
helix. Proline facilitates the formation of the helical
conformation of each αchain because its ring structure
causes “kinks”in the peptide chain. Glycine, the
smallest amino acid, is found in every third position of
the polypeptide chain. It fits into the restricted spaces
where the three chains of the helix come together. 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,).
Most of the α-chain can be regarded as a
polytripeptide whose sequence can be represented as
(–Gly–Pro–Hyp–)
Endoplasmic Reticulum
mRNA attached to ER
protein synthesized into ER
lumen
cotranslational and posttranslational modifications
3 proto-a-chains form
soluble procollagen
moved to golgi apparatus
Golgi Apparatus
packed into secretion vesicles
fuse with membrane
Outside Cell
procollagen processed by
enzymes outside cell
assemble into collagen fibers
collagen fibrils form lateral
Interactions of triple helices
Collagen biosynthesis
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Tropocollagen has a mass of about 285 kdal and
consist of three polypeptide chains.
Tropocollagen -280 nm long -head & tail region
30% glycine, 30% proline& hydroxyproline
re-aggregate -native collagen (64nm)
non Covalent hydrogen bonding between the
three αchain is via hydroxyproline.
tropocollagenpolarized in fiber, 1/4 staggered
array –period accounted for by gaps fall in dark
bands
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Collagen fibres exhibit crosssstriations every
640A.
The length of the tropocollagenmolecule s
2800A.
There is a gap of 400oA between the end of
one tropocollagenand the start of another.
This gap play an important role in
mineralization process.
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Lysyl oxidase is an extracellular copper
enzyme that catalyzes formation of aldehydes
from lysine residues in collagen and elastin
precursors. These aldehydes are highly
reactive, and undergo spontaneous chemical
reactions with other lysyl oxidase-derived
aldehyde residues, or with unmodified lysine
residues. This results in cross-linking
collagen and elastin, which is essential for
stabilization of collagen fibrils and for the
integrity and elasticity of mature elastin.
Complex cross-links are formed in collagen
called Pyridinoline which is derived from
three lysine residues.
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The temperature at which half of the helical structure is
lost is called the melting temperature™.
The Tm of tropocollagenis a criterion of the stability of its
helical structure. Tm depends on the body temperature of
the source species. collagens from icefishhas the lowest
Tm while warm blooded animals have the highest Tm. This
difference in thermal stability is correlated with the
contents of iminoacid (prolineand hydroxyproline) in the
collagen. The higher the iminoacid content , the more
stable the helix. Tm of (pro-pro-Gly) is 24C while poly
(Pro-Hyp-Gly) is 580C indicating hydroxylation stabilizes
triple helix.
The experiments using αα\-bipyridylan iron chelatorwhich
inhibit hydroxylation shows that without hydroxylation
triple helix formation does not occur.
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Source:
Clostridium
histolyticum
I.U.B.: 3.4.24.3
Crude collagenase preparations contain not only several collagenases
but also a sulfhydryl protease, clostripain, a trypsin-like enzyme, and
an aminopeptidase. This combination of collagenolytic and
proteolytic activities is effective at breaking down intercellular
matrices, the essential part of tissue dissociation. One component of
the complex is a hydrolytic enzyme which degrades the helical
regions in native collagen preferentially at the Y-Gly bond in the
sequence Pro-Y-Gly-Pro- where Y is most frequently a neutral amino
acid. This cleavage yields products susceptible to further peptidase
digestion. Crude collagenase is inhibited by metal chelating agents
such as cysteine, EDTA or o-phenanthroline but not DFP. It is also
inhibited by α2-macroglobulin, a large plasma glycoprotein. Ca2+ is
required for enzyme activity. Particular enzymatic profiles of each
collagenase have been correlated with the tissues from which the
cells for study were obtained (or with the uses to which the cells are
put) and as a result of the correlations several types of crude
collagenases have been established by Worthington: Types 1, 2, 3,
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Type 1 crude collagenase has the original
balance of collagenase, caseinase, clostripain
and tryptic activities.
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Type 2 contains higher relative levels of
protease activity particularly clostripain.
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Type 3 contains lowest levels of secondary
proteases.
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Type 4 is designed to be especially low in
tryptic activity to limit damage to membrane
proteins and receptors.
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Elastin is a protein in connective tissue that
is elastic and allows many tissues in the body
to resume their shape after stretching or
contracting. Elastin helps skin to return to its
original position when it is poked or pinched.
Elastin is also an important load-bearing
tissue in the bodies of vertebrates and used
in places where mechanical energy is required
to be stored. In humans, elastin is encoded
by the ELN gene.
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Elastic fiber is composed of the protein fibrillin and
elastin made of simple amino acids such
as glycine, valine, alanine, and proline.
Elastin
is
made
by
linking
many
soluble tropoelastin protein molecules, in a
reaction catalyzed by lysyl oxidase, to make a
massive insoluble, durable cross-linked array. The
amino acid responsible for these cross-links
is lysine. Tropoelastin is a specialized protein with
a molecular weight of 64 to 66 kDa, and an
irregular or random coil conformation made up of
830 amino acids.
Desmosine and isodesmosine are types of links for
the
tropoelastin
molecules.
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Elastin serves an important function in arteries as
a medium for pressure wave propagation to
help blood flow and is particularly abundant in
large elastic blood vessels such as the aorta.
Elastin is also very important in the lungs, elastic
ligaments, the skin, and the bladder, elastic
cartilage.
It is present in all vertebrates above the jawless
fish.
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protein Mr 64 to 66 kDa
composed of the amino acids glycine, valine,
alanine, and proline
cross-linked tropoelastin monomers
first secreted as soluble precursors (tropoelastin)
assembly and crosslinking of tropoelastin
monomers
form insoluble elastin matrix into functional
fibres
◦ lysine residues in the cross-linking domain of secreted
tropoelastin rapidly cross-linked (both inter- and intramolecularly by lysyl oxidase)
◦ hydrophobic segments - elastic properties
◦ α-helical segments (alanine- and lysine-rich) - form
cross-links between adjacent molecules