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1

Extracellular Matrix

The extracellular matrix (ECM) is the ___ ___ component present within all tissues and organs

ECM provides not only essential physical ____ for the cellular constituents but also initiates crucial ____ and ____ cues that are required for tissue ____, ___and ____.

ECM is a complex network of_____(such as ____ or ____) and ____(such as ____ or ____) secreted by ___.

Each ____ has an ECM with a unique composition and topology that is generated during tissue development through a ___ and____, biochemical and biophysical ____between the various cellular components

  • In skin, loose connective tissue consists of ECM in which fibroblasts, blood vessels and other components are distributed.
  • Tendon and cartilage consist largely of ____
  • Brain and spinal cord are composed primarily of cells with __ ___ ECM

The ECM also forms a _____ ___ _____ on which layers of ____ ___ ___

The extracellular matrix (ECM) is the non-cellular component present within all tissues and organs ECM provides not only essential physical scaffolding for the cellular constituents but also initiates crucial biochemical and biomechanical cues that are required for tissue morphogenesis, differentiation and homeostasis ECM is a complex network of polysaccharides (such as glycosaminoglycans or cellulose) and proteins (such as collagen and elastin) secreted by cells Each tissue has an ECM with a unique composition and topology that is generated during tissue development through a dynamic and reciprocal, biochemical and biophysical dialogue between the various cellular components In skin, loose connective tissue consists of ECM in which fibroblasts, blood vessels and other components are distributed. Tendon and cartilage consist largely of ECM Brain and spinal cord are composed primarily of cells with very little ECM The ECM also forms a sheetlike basal laminae on which layers of epithelial cells rest.

2

Components of the ECM

The ECM is composed of two main classes of macromolecules: _____(PGs) and ___ ___.

Fibrous structural proteins

___ ____ ____ _____

 Some fibrous proteins (____ and _____) also serve as ____proteins that bind to other components of the extracellular matrix (___, ____) and to ___ ___ ___, thereby __-___ the matrix to the___ ___

Proteoglycans - consists of a __ ___ covalently attached to many ___, ___ chains of ______

The ECM is composed of two main classes of macromolecules: proteoglycans (PGs) and fibrous proteins Fibrous structural proteins Collagen Elastin Fibronectin Laminin Some fibrous proteins (fibronectin and laminin) also serve as adhesion proteins that bind to other components of the extracellular matrix (collagen, polysaccharides) and to cell-surface receptors, thereby cross-link the matrix to the cell membrane Proteoglycans - consists of a core protein covalently attached to many long, linear chains of glycosaminoglycans

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Cell Adhesion Molecules (CAMs)

Many functions of the matrix involve CAMs, which are ___ ___ ___ that mediate __-___and ___-___ adhesion

There are 5 major classes of CAMs - ____ ___ ___ ___ ___

CAMs bind directly to components of the ___ and the ____

CAMs can also interact with ___ on neighbouring cells

CAMs provide mechanism for ____ between cells via both ____ signals and through signals generated via ____.

The principal class of CAMs that mediate cell-matrix adhesion is the ___

Cell Adhesion Molecules (CAMs) Many functions of the matrix involve CAMs, which are integral membrane proteins that mediate cell-cell and cell-matrix adhesion There are 5 major classes of CAMs - integrins, cadherins, selectins, immunoglobulin (Ig) superfamily, and mucins CAMs bind directly to components of the ECM and the cytoskeleton CAMs can also interact with CAMs on neighbouring cells CAMs provide mechanism for signaling between cells via both internal signals and through signals generated via ECM The principal class of CAMs that mediate cell-matrix adhesion is the integrins

4

Functions of ECM

  • Fcn as ___ ___
    • Tracks to direct migratory cells
    • [] gradients for haptotatic migration
    • Need to attach to something to ____. ECM provides that attachment
  • Provides ____
    • defines tissue boundaries
    • Provides ___ and ____ to developing organs
    • Degraded by invasive cells during development and diseaae
  • ___ ____ to their____
    • Controls spatial distribution of ECM-bound surface molecules
    • facillitates Cross talk bw GFR and ECM Receptors
  • ____and ____ ____
    • allows for spatio-temporal regulation of factor release
    • organizes morphogen gradients
    • mediates release of factors in presense of appropriate cell mediated forces or proteolytic degredation
  • ____s and ___s ____ signals
    • Defines mechanical properties permissive/instructive to cell differentiation
    • Activates intracellular signaling thru interaction with cell surface receptors
    • Engages cytoskeletal machinery and synergizes with GF signaling

  • Fcn as adhesive substrate
    • tracks to direct migratory cells
    • [] gradients for haptotatic migration
    • Need to attach to something to migrate. ECM provides that attachment
  • Provides Structure
    • defines tissue boundaries
    • Provides integrity and elasticity to developing organs
    • Degraded by invasive cells during development and diseaae
  • Presents GF to their receptors
    • Controls spatial distribution of ECM-bound surface molecules
    • facillitates Cross talk bw GFR and ECM Receptors
  • Sequestors and stores GF
    • allows for spatio-temporal regulation of factor release
    • organizes morphogen gradients
    • mediates release of factors in presense of appropriate cell mediated forces or proteolytic degredation
  • Senses and transduces mechanical signals
    • Defines mechanical properties permissive/instructive to cell differentiation
    • Activates intracellular signaling thru interaction with cell surface receptors
    • Engages cytoskeletal machinery and synergizes with GF signaling

5

Degradation of ECM

Timely degradation of ECM is an important feature of ____, ___ ,___ ___and ____.

Various types of proteinases are implicated in ECM degradation, but the major enzymes are considered to be ______), also called _____

There are ____different MMPs in humans.

MMP expression is tightly regulated and is ____ controlled by inflammatory cytokines, growth factors, hormones, cell–cell and cell–matrix interaction.

MMP activities are also regulated by activation of the precursor ____and inhibition by endogenous inhibitors, ___ ___ _____ ____ (TIMPs).

Timely degradation of ECM is an important feature of development, morphogenesis, tissue repair and remodeling. Various types of proteinases are implicated in ECM degradation, but the major enzymes are considered to be matrix metalloproteinases (MMPs), also called matrixins. There are 23 different MMPs in humans. MMP expression is tightly regulated and is transcriptionally controlled by inflammatory cytokines, growth factors, hormones, cell–cell and cell–matrix interaction. MMP activities are also regulated by activation of the precursor zymogens and inhibition by endogenous inhibitors, tissue inhibitors of metalloproteinases (TIMPs).

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Degradation of ECM

MMPs may affect ___ ___ by changing the cells from an ___ to ___ ____ phenotype and by _____ the ECM.

MMPs may alter ECM ______ leading to cell ____, ____s, or ____.

MMPs may modulate the activity of biologically ____ molecules such as ___ ____ or ___ ___ ____by ___ them or ____ them from the ECM.

MMPs may affect cell migration by changing the cells from an adhesive to non adhesive phenotype and by degrading the ECM. MMPs may alter ECM microenvironment leading to cell proliferation, apoptosis, or morphogenesis. MMPs may modulate the activity of biologically active molecules such as growth factors or growth factor receptors by cleaving them or releasing them from the ECM.

7

Collagen

The major ____fibrous protein in the extracellular matrix and in ___ ___.

Primarily produced by ___, but also by ___ cells and ___ cells

Most ___ proteins in mammals – constitute ___% of total protein mass

___ different types of collagen have been identified in vertebrates, but 80 – 90 percent of the collagen in the body consists of types _ __ ___.

These collagen molecules pack together to form ___ ___ ___ of similar structure.

Type IV, in contrast, forms a ___ ___ ___.

 Several other types ___ with __ ___ collagens, linking them to ___ ___ or to other ___ components.

Collagen The major insoluble fibrous protein in the extracellular matrix and in connective tissue Primarily produced by fibroblasts, but also by muscle cells and epithelial cells Most abundant proteins in mammals – constitute 25% of total protein mass Twenty-eight different types of collagen have been identified in vertebrates, but 80 – 90 percent of the collagen in the body consists of types I, II, and III These collagen molecules pack together to form long thin fibrils of similar structure. Type IV, in contrast, forms a two-dimensional reticulum Several other types associate with fibril-type collagens, linking them to each other or to other matrix components.

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Basic structural unit of collagen type I

Its fundamental structural unit is a 300 nm long, 1.5 nm in diameter thin protein in which____ collagen polypeptide chains, called___ chains, are ___ around one another in a ropelike ____.

Each chain contains precisely 1050 amino acids wound around one another in a characteristic ___handed triple helix

Note: All collagens were eventually shown to contain three-stranded helical segments of similar structure; the unique properties of each type of collagen are due mainly to ____ that___ the triple helix and that ___ into other kinds of three-dimensional structures.

Each α chain is arranged as a ___-handed helix, with three amino acids per turn and with ____ as every third amino acid. Therefore, an α chain is composed of a series of triplet Gly-X-Y sequences, in which X and Y can be ___ amino acid. The amino acids in the X and Y positions of collagen are often ___ (28%) and ____ (38%) Overall, collagen contains ~33% glycine and 21% proline/hydroxyproline

Glycine is the only amino acid ___ enough to occupy the ___ ___ of the triple helix

Proline, because of its ring structure, ____ the helical conformation in each __ chain

The ladder of recurrent N–H(Gly)⋯O=C(Xaa) ___ ___ that form between adjacent ___ chains holds the ___ ___ intact

Basic structural unit of collagen type I Its fundamental structural unit is a 300 nm long, 1.5 nm in diameter thin protein in which three collagen polypeptide chains, called α chains, are wound around one another in a ropelike superhelix Each chain contains precisely 1050 amino acids wound around one another in a characteristic right-handed triple helix Note: All collagens were eventually shown to contain three-stranded helical segments of similar structure; the unique properties of each type of collagen are due mainly to segments that interrupt the triple helix and that fold into other kinds of three-dimensional structures. Each α chain is arranged as a left-handed helix, with three amino acids per turn and with glycine as every third amino acid. Therefore, an α chain is composed of a series of triplet Gly-X-Y sequences, in which X and Y can be any amino acid. The amino acids in the X and Y positions of collagen are often proline (28%) and hydroxyproline (38%) Overall, collagen contains ~33% glycine and 21% proline/hydroxyproline Glycine is the only amino acid small enough to occupy the crowded interior of the triple helix Proline, because of its ring structure, stabilizes the helical conformation in each α chain The ladder of recurrent N–H(Gly)⋯O=C(Xaa) hydrogen bonds that form between adjacent α chains holds the triple helix intact

9

Biosynthesis and hierarchy of collagen

Collagen biosynthesis and assembly follows the normal pathway for a secreted protein

The collagen polypeptides are synthesized as longer precursors called ____chains on ___membrane-bound____; the growing peptide chains are co-translationally ____ into the ___ of ER

In the lumen of ER, the pro α chains undergo ____.

  • Selected prolines and lysines are ____to form hydroxyproline and hydroxylysine Some of the hydroxylysines are ____ 
  • In the ER and golgi, each pro-α chain then ____ with two others to form a ____-bonded, ___-stranded, helical molecule known as ____

Procollagen is then___ into the extracellular space

Procollagen ___ remove the _erminal and _-terminal propeptides forming ___.

This allows the collagen molecules to polymerize into normal ____ in the extracellular space

Collagen fibrils have characteristic ___-____ every 67 nm, reflecting the regularly staggered packing of the individual ___ ____ in the fibril.

Collagen fibrils provide great ___ ___to the ___ ____

Biosynthesis and hierarchy of collagen Collagen biosynthesis and assembly follows the normal pathway for a secreted protein The collagen polypeptides are synthesized as longer precursors called pro α chains on ER membrane-bound ribosomes; the growing peptide chains are co-translationally transported into the lumen of ER In the lumen of ER, the pro α chains undergo processing Selected prolines and lysines are hydroxylated to form hydroxyproline and hydroxylysine Some of the hydroxylysines are glycosylated In the ER and golgi, each pro-α chain then combines with two others to form a hydrogen-bonded, triple-stranded, helical molecule known as procollagen Procollagen is then secreted into the extracellular space Procollagen peptidases remove the N-terminal and C-terminal propeptides forming collagen This allows the collagen molecules to polymerize into normal fibrils in the extracellular space Collagen fibrils have characteristic cross-striations every 67 nm, reflecting the regularly staggered packing of the individual collagen molecules in the fibril Collagen fibrils provide great tensile strength to the connective tissues

10

Effect of vitamin C deficiency on collagen

The ____ reactions of proline and lysine residues require___ ___ (ascorbic acid) as a ____of the enzymes___ ____ and ___ ____.

In the absence of vitamin C, the melting temperature of collagen drops from ___ to ___ because of the loss of____ ___ ___ formation caused by the lack of hydroxyproline residues.

In ____, a condition caused by vitamin C deficiency, collagen ____ are not properly formed. As a result, the tissues, especially those of the __ and ___ ___, become ___. This leads to ____ in the skin and mucous membranes, which is especially noticeable in the ____.

The hydroxylation reactions of proline and lysine residues require vitamin C (ascorbic acid) as a cofactor of the enzymes prolyl hydroxylase and lysyl hydroxylase. In the absence of vitamin C, the melting temperature of collagen drops from 42 to 24 because of the loss of interstrand hydrogen bond formation caused by the lack of hydroxyproline residues. In scurvy, a condition caused by vitamin C deficiency, collagen fibers are not properly formed. As a result, the tissues, especially those of the skin and blood vessels, become fragile. This leads to bleeding in the skin and mucous membranes, which is especially noticeable in the gums.

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Collagen Type IV

Type IV collagen occurs only in the ___ ___ and is comprised of α-chains

Each chain contains three structurally distinct domains

  • an N-terminal domain rich in ___ and ____ residues
  • a major collagenous _____ triple repeats of ~1,400 residues
  • a ~230-residue long C-terminal _____ (NC1) domain

NC1 domains can be considered as the ___ ___ for the molecular assembly of the collagen IV molecules. They are the sites where ___ ____ formation is initiated

Cysteine- and lysine-rich residues at the N terminus are essential for ___ ___ of ___ triple-helical molecules through ____ ___ and ___-____crosslinks.

Another characteristic feature of collagen IV is the presence of 21–26 ____ in the collagenous Gly-X-Y triple repeats, which provide molecular___ for network formation and serve as sites for __ __and ___ ____

Once secreted into the ECM, the triple-helical molecules ___ ___ to form ___ ___ providing a molecular scaffold onto which other___ components such as laminins, perlecans, and proteoglycans can interact.

This is not the only type of collagen in basal lamina but it is the ____ form found

Collagen Type IV Type IV collagen occurs only in the basement membranes and is comprised of α-chains Each chain contains three structurally distinct domains an N-terminal domain rich in cysteine and lysine residues a major collagenous Gly-X-Y triple repeats of ~1,400 residues a ~230-residue long C-terminal noncollagenous (NC1) domain NC1 domains can be considered as the initial directors for the molecular assembly of the collagen IV molecules. They are the sites where triple-helical formation is initiated Cysteine- and lysine-rich residues at the N terminus are essential for interchain crosslinking of four triple-helical molecules through disulfide bonds and lysine-hydroxylysine crosslinks. Another characteristic feature of collagen IV is the presence of 21–26 interruptions in the collagenous Gly-X-Y triple repeats, which provide molecular flexibility for network formation and serve as sites for cell binding and interchain crosslinking Once secreted into the ECM, the triple-helical molecules self-associate to form distinct networks providing a molecular scaffold onto which other ECM components such as laminins, perlecans, and proteoglycans can interact. This is not the only type of collagen in basal lamina but it is the predominant form found

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Fibril-associated collagens

(a) Type IX collagen

  • Consists of ___ long triple helices connected by a _-__ ___ ___.
  • The protruding nonhelical domains are thought to anchor the fibril to ____ and other components of the ___.
  • The ____ triple-helical structure of type IX collagen prevents it from assembling into ____; instead, these collagens associate with ___ formed from other collagen types and thus are called fibril-associated collagens

(b) Type VI collagen

  • Consists of ___ triple helices, about 60 nm long, with ___ domains at either end. The globular domains of several type VI molecules ___ together, giving a “_________” appearance to the type VI fibril

Fibril-associated collagens (a) Type IX collagen Consists of two long triple helices connected by a non-helical flexible kink. The protruding nonhelical domains are thought to anchor the fibril to proteoglycans and other components of the matrix The interrupted triple-helical structure of type IX collagen prevents it from assembling into fibrils; instead, these collagens associate with fibrils formed from other collagen types and thus are called fibril-associated collagens (b) Type VI collagen Consists of thin triple helices, about 60 nm long, with globular domains at either end. The globular domains of several type VI molecules bind together, giving a “beads-on-a-string” appearance to the type VI fibril

13

Distribution and origin of a few collagen subtypes Know which collagen types are found in: Ordinary connective tissue _ _

Bone_ _

Dentin _ _ _

Basement membrane/ basal lamina _

Predom type in Bone, Tissue, Dentin: Type I

Type IV is the one found in the basement membrane

Know which collagen types are found in: Ordinary connective tissue Bone Dentin Basement membrane/ basal lamina

Bone I V

Dentin I III V

Basement membrane/ basal lamina IV

Predom type in Bone, Tissue, Dentin: Type I

Type IV is the one found in the basement membrane

14

ECM in teeth

In tooth development, three types of ECM structures play critical roles in morphogenesis.

  • (1) Basement membranes
    • Consist of a unique set of ECM proteins and serve as a ___ barrier and a ____structure for reciprocal ___ between the dental ___ and ___ in early development. The dental epithelium and mesenchyme differentiate to ____ matrix-secreting ____ and ___matrix-secreting ___.
  • (2) Dentin Contains ~__% minerals and __% organic matrix which mainly composed of collagen _ which provides a ___ for dentin____. Many __-____s dentin matrix proteins are also required for _____n in these tissues.
  • (3) Enamel Consists of __% of mineral but only traces of____matrix. Mineralization in enamel matrix is formed primary through activities of ____ ____ proteins.

In tooth development, three types of ECM structures play critical roles in morphogenesis. Basement membranes Consist of a unique set of ECM proteins and serve as a physical barrier and a regulatory structure for reciprocal signaling between the dental epithelium and mesenchyme in early development. The dental epithelium and mesenchyme differentiate to enamel matrix-secreting ameloblasts and dentin matrix-secreting odontoblasts. (2) Dentin Contains ~80% minerals and 20% organic matrix which mainly composed of collagen I which provides a scaffold for dentin mineralization. Many non-collagenous dentin matrix proteins are also required for mineralization in these tissues. (3) Enamel Consists of 96% of mineral but only traces of organic matrix. Mineralization in enamel matrix is formed primary through activities of non-collagenous proteins.

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Elastin

Elastic fibers are major extracellular matrix assemblies that provide ___ and____ to a range of tissues which undergo periodic or frequent ____, such as aorta, lung, and elastic ligaments

Elastic fibers consist of two morphologically distinct components

  • ____, which is a ___ ____ polymer of the monomeric secreted form of the protein ____, is the major component
  • ____, which is visualized as small, 10–15-nm structures that localize to the ____ of the fiber, is the minor component

Based on ultrastructural studies, microfibrils are thought to provide a ____ that facilitates elastin molecular ____and subsequent______

Elastic fibers are major extracellular matrix assemblies that provide elasticity and resilience to a range of tissues which undergo periodic or frequent stretching, such as aorta, lung, and elastic ligaments Elastic fibers consist of two morphologically distinct components Elastin, which is a cross-linked polymer of the monomeric secreted form of the protein tropoelastin, is the major component Microfibrils, which is visualized as small, 10–15-nm structures that localize to the periphery of the fiber, is the minor component

Based on ultrastructural studies, microfibrils are thought to provide a scaffold that facilitates elastin molecular alignment and subsequent cross-linking.

16

Elastin

Elastin is a highly _____protein (about 750 amino acids long), which, like collagen, is unusually rich in ___ and ___.

Unlike collagen, elastin is not ____ and contains some _____ but no ____.

Soluble tropoelastin and microfibrils are secreted into the ____ space close to the __ ___.

The microfibrillar component works as a scaffold for the ____of tropoelastin and serve to___ the tropoelastin molecules into the correct ____ for subsequent ___-___

Cross-linking of tropoelastin generates an extensive ____of elastin fibers and ___s. The cross-links are formed between____.

Elastin is a highly hydrophobic protein (about 750 amino acids long), which, like collagen, is unusually rich in proline and glycine Unlike collagen, elastin is not glycosylated and contains some hydroxy-proline but no hydroxylysine Soluble tropoelastin and microfibrils are secreted into the extracellular space close to the cell surface The microfibrillar component works as a scaffold for the deposition of tropoelastin and serve to align the tropoelastin molecules into the correct orientation for subsequent cross-linking Cross-linking of tropoelastin generates an extensive network of elastin fibers and sheets. The cross-links are formed between lysines

17

Structure of elastin

Tropoelastin is composed largely of two types of short segments (domains) that ____ along the polypeptide chain:

  • ____ segments rich in___,___ , ____ , which are responsible for the ____ properties of the molecule
  • ___- and___-rich ____ α-helical segments, which form ___ __ between adjacent molecules
  • Each segment is encoded by a separate ___

.When the elastic fibers are stretched the repeating hydrophobic domains of the molecule are ____ to the surrounding aqueous environment. This in turn, leads to a ____ in the entropy of water molecules which will have to rearrange around the hydrophobic domains.

When the stretching force is removed the elastin readily returns to its original form since this allows an ___ in the entropy of water molecules around the hydrophobic domains.

Tropoelastin is composed largely of two types of short segments (domains) that alternate along the polypeptide chain: hydrophobic segments rich in valine, proline and glycine, which are responsible for the elastic properties of the molecule alanine- and lysine-rich hydrophilic α-helical segments, which form cross-links between adjacent molecules Each segment is encoded by a separate exon. When the elastic fibers are stretched the repeating hydrophobic domains of the molecule are exposed to the surrounding aqueous environment. This in turn, leads to a decrease in the entropy of water molecules which will have to rearrange around the hydrophobic domains. When the stretching force is removed the elastin readily returns to its original form since this allows an increase in the entropy of water molecules around the hydrophobic domains.

18

Elastogenesis

Immediately after translation, the tropoelastin molecule is ____ by its molecular____in the rough ____ ____.

This association, which prevents the ____ ____ of tropoelastin, persists in the ___ until the ____ of the complex.

In the extracellular space, the complex is localized on the ___ ___.

When it comes in contact with a nascent elastic fiber, the chaperone interacts with ____ of the ____ component leading to the local _____of the tropoelastin molecule. While the chaperone is ___, the tropoelastin molecule is ___ correctly and promptly modified by ___ ____.

Finally, it is _____ in the elastic network by ____ ____, and consequently, elastin grows within the microfibrillar scaffold.

Immediately after translation, the tropoelastin molecule is captured by its molecular chaperone in the rough endoplasmic reticulum.

This association, which prevents the prematurate aggregation of tropoelastin, persists in the Golgi until the excretion of the complex.

In the extracellular space, the complex is localized on the cell surface.

When it comes in contact with a nascent elastic fiber, the chaperone interacts with galactosugars of the microfibrillar component leading to the local release of the tropoelastin molecule. While the chaperone is recycled, the tropoelastin molecule is aligned correctly and promptly modified by lysyl oxidase. Finally, it is incorporated in the elastic network by irreversible polymerization, and consequently, elastin grows within the microfibrillar scaffold.

19

Abnormal elastin and disease

____ ____ ____  (SVAS)

  • a disease that causes significant ____ of the large ___.
  • ___ or ___ ___ occurring in the elastin gene constitute the genetic defect
  • The translated tropoelastin is ____ and thus lacks some ______ domains as well as the ___ ____ region resulting in deposition of abnormal elastic fibers.

Supravalvular aortic stenosis (SVAS) a disease that causes significant narrowing of the large arteries Translocation or point mutations occurring in the elastin gene constitute the genetic defect The translated tropoelastin is truncated and thus lacks some cross-link domains as well as the C-terminal region resulting in deposition of abnormal elastic fibers.

20

Laminin

Laminins are structural components of ___ ___.

In addition to providing ____ support, laminins play important roles in tissue ___ and ____ by regulating tissue ____, cell ____, ___ and matrix-mediated ___

There are ___ known members of the laminin family which exhibit some tissue ____and their expression is often ______ regulated

Laminins are structural components of basement membranes In addition to providing structural support, laminins play important roles in tissue morphogenesis and homeostasis by regulating tissue architecture, cell adhesion, migration and matrix-mediated signaling There are 16 known members of the laminin family which exhibit some tissue specificity and their expression is often developmentally regulated

21

Laminin

Laminins are ____ proteins composed of _ _ _-subunits.

The major feature of the laminin structure is the ___ ___alpha helix, which joins the ___ chains together and forms a __ __.

Laminin heterotrimers are relatively ___ proteins (with molecular masses ranging from 400 to 900 kDa) and exist as __ ___ molecules with _or _ short arms and _ long arm

All three chains have extensions at the____ terminal end. Only the alpha chain has a significant ___-terminal extension past the ____ structure.

It is the laminin extensions that allow laminin to bind to other components within the___ and provide ____ to the structure.

Components of the ECM that are bound by laminin include ___ ____ ____

Laminin Laminins are heterotrimeric proteins composed of α-, β- and γ-subunits. The major feature of the laminin structure is the coiled coil alpha helix, which joins the three chains together and forms a rigid rod. Laminin heterotrimers are relatively large proteins (with molecular masses ranging from 400 to 900 kDa) and exist as cross-shaped molecules with two or three short arms and one long arm All three chains have extensions at the amino terminal end. Only the alpha chain has a significant carboxy-terminal extension past the rodlike structure. It is the laminin extensions that allow laminin to bind to other components within the ECM and provide stability to the structure. Components of the ECM that are bound by laminin include collagen, integrins and proteoglycans

22

Deposition of laminin heterotrimers

Despite their relatively uniform structure, laminin heterotrimers are deposited into ____ ____ or patterns in the ___ ___of cultured cells

In the matrix of non-migrating keratinocytes, the α3 laminin subunit appears in a rosette-like pattern. In alveolar epithelial cells of the lung, the α3 laminin subunit appears in fibrillar arrays. In immortalized endothelial cells, the α4 laminin subunit localizes to focal-adhesion-like structures.

Despite their relatively uniform structure, laminin heterotrimers are deposited into diverse arrays or patterns in the extracellular matrix of cultured cells In the matrix of non-migrating keratinocytes, the α3 laminin subunit appears in a rosette-like pattern. In alveolar epithelial cells of the lung, the α3 laminin subunit appears in fibrillar arrays. In immortalized endothelial cells, the α4 laminin subunit localizes to focal-adhesion-like structures.

23

Abnormal laminin and disease

___ ___ ___

Results from a defect in laminin, which serves as a component of the___ that links the ___ cell ___ to the ___ ___.

Lack of this bridge triggers muscle cell ____s, which results in ___ muscles.

Congenital Muscular Dystrophy (CMD) Results from a defect in laminin, which serves as a component of the bridge that links the muscle cell cytoskeleton to the extracellular matrix. Lack of this bridge triggers muscle cell apoptosis, which results in weakened muscles.