MSK_MT1_TBL3 (Fibrous Proteins)

Question 1

Big Picture: Types of Connective Tissue (CT) [3]

Answer 1

1. Embryonic/Mesenchyme CT: stem cells/ makes all CT
2. Connective Tissue Proper
   • Loose CT: found beneath epithelia, covers all surfaces (inside and out), glands, and surrounds small blood vessels
   • Dense CT
     
     • Regular: functional component of tendons, ligaments, and aponeuroses
     • Irregular: surrounds organs and skin as s_hock absorber,_ mostly collagen fibers and fibroblasts
3. Specialized Connective Tissue (not covered): Cartilage, Blood, Bone, hemopoietic tissue, lymphatic, adipose

Question 2

Outside Cell Organization (3)

Answer 2

1. Extracellular Matrix (ECM)
2. Key Fibrous Proteins
3. Resident Cells
   
   1. Mesenchymal cells (Stem)
   2. Macrophages cells (Immune)
   3. Adipocyte cells (Fat)
   4. Fibroblasts cells (Make Collagen)

Question 3

ECM composed of (3)

Answer 3

1. basement membrane: thin, dense sheets that surround most animal tissues
2. interstitial matrix: gel between cells* & *structures
3. ground substance: jelly (with NO collogen)

Question 4

Types of Fiberous Proetin found outside the cell… (4)

Answer 4

1. Structural
   
   • Collagen
2. Flexible
   
   • Elastin
   • Fibrillin
3. Adhesive
   
   • Fibronectin
   • Laminin
   • Karatin

• Others
  
  • glycosoaminoglycans
  • proteoglycans
  • polysaccarides

Question 5

Collagen Structure

Answer 5

• Collagen = 42 fibrous protein genes
  
  • 25% of total protein mass
• fibroblast synthesize & secrete in ECM
• “triple helix” structure: contains three long α- helicies
• Large amounts of proline, lysine, and glycine with repeating units of Gly-X-Z.
  
  • Glycine is internal to the helix
  • X and Z will be most likely hydroxy proline and hydroxy lysine.

Question 6

Collagen Structural Components (small → big)

Answer 6

collagen fibril → twisting self assembly → collegen molecule (rope) → triple helix

Question 7

Collagen Types

Answer 7

Fibrous collagens (type I, II and III), which constitute about 70% of the total body collagen, have a fibrillar structure.

Question 8

Type I Collagen

Answer 8

1. skin
2. bone
3. tendons
4. cornea
5. internal organs

Defect = osteogenesis imperfecta

Question 9

Type II Collagen

Answer 9

1. cartilage
2. intervertebral discs
3. vitreous humor (eye)

Question 10

Type III Collagen

Answer 10

1. skin
2. blood vessels
3. lymph nodes, dermis, early phases of wound repair

Defect = Ehlers-Danlos syndrome

Question 11

Type IV Collagen

Answer 11

1. basement membranes : flexible, sheet-like networks and is present within all basement membranes.
2. basal lamina (beneath epithelial layer)
3. lens
4. cochlea

genetic defects = Alport Syndrome

Question 12

Collagen Synthesis Overview: In the Nucleus

Answer 12

Collagen gene → DNA Synthesis → Transcription (mRNA) →

Signal Sequence Directs Growing polypeptide chain into Endoplasmic Reticulum →

Question 13

Collagen Synthesis Overview: In the ER

Answer 13

Pre-procollagen (Translation/protein synthesis) →

Signal sequence is cleaved at ends to = procollagen α- chain →

Prolyl or Lysyl Hydroxylation (Vitamin C dependent)→

Glycosylation (galactosyl and glucosyl sugars) of hydroxy lysyl →

Disulfide bond formation by Cys side chains →

pro α- chain TO procollagen triple helix (procollagen) with nonhelical propeptides at the end

__________________________________

TRANSPORT of soluble procollagen to Golgi

Question 14

Collagen Synthesis Overview: In the Golgi

Answer 14

Golgi packages soluble procollagen in secretory vesicles →

Secretory vesicles transport soluble procollagen to cell surface →

via special COPII vesicles, XXL

Question 15

Collagen Synthesis Overview: Extracellular Space

Answer 15

procollagen peptidases CLEAVE procollagen → Tropocollagen →

Collagen fibril self-assembly →

Covalent crosslinking between triple helix by lysyl oxidase (COPPER dependant) →

Collagen fibers formation

Question 16

Synthesis and Secretion of Collagen: Nucelus and RER

Answer 16

1. mRNA transcribed
2. Single α-chains synthesized on rough ER ribosome
   
   • Contain signal recognition (to bind SRP)
   • makes a Pre-procollagen
3. Enter ER lumen (pro-α-chains)
4. Some prolines and lysines are hydroxylated by using vitamin C.
   
   • (deficiency → scurvy)
5. Some hydroxylysines are glycosylated (addition of sugar)

Question 17

Collagen Synthesis in Endoplasmic Reticulum and Golgi

Answer 17

1. RER: The 3 α-chains begin to align in zipper fashion
2. Form disulfide bonds that stabilize α-chains (especially at C-terminus)
3. prolyl-peptide isomerase enzymes rearrange Prolines
4. Cleavage of N-terminus = “procollogen”
   
   • (Three α-chains combine= Triple helix formation)

Question 18

Collagen Synthesis: Extracellular Modifications ( in ER)

Answer 18

Once outside (ECM) Collagen fibrils form:

1. Tropocollagen much less soluble than procollagen
2. Fibrils self assemble
3. Strengthened by lysine crosslinking via lysyl oxidase
   
   • Requires copper (Cu+2) as cofactor
   • Hydrogen Peroxide (H2O2) is the side product of rxn catalyzed by Lysyl Oxidase.
4. Collagen fibers made = bundles of triple helices

Question 19

Crosslinking to ↑↑↑ strength

Answer 19

Question 20

Collegen Disease: Osteogenesis Imperfecta (Brittle Bone Disease)

Answer 20

• genetic autosomal dominant
• Defective collagen production, ranging in severity of osteoporosis and fractures

Type I:

• MUTATION in COL1A1 or COL1A2 genes ( code for α-chains)
  
  • Glycine (in Gly-X-Y) REPLACED by AA w/ bulky side chain.
  • collagen/elastin fibers thicken & clump = ↓↓↓ of Type I collagen

Type II (lethal in utero)

Type II and IV (>>>>> severe than type I)

Multiple, recurrent fractures with minimal trauma, blue sclera, bad hearnig, bad teeth, bony deformity and short stature.

Question 21

Collegen Disease: Ehlers Danlos Syndrome

Answer 21

Family of genetic connective tissue disorders

via defective collagen synthesis

Classic Type

Autosomal dominant (often de novo mutation)

COL5A1 or COL5A2 genes (type V collagen)

Type V interacts with other collagens

Joint hypermobility and hyperensemble skin

Easy bruising, thin, wide scars (cigarette paper scars)

Vascular type

Autosomal dominant

COL3A1 gene (type III collagen)

Skin, blood vessels

Thin skin, easy bruising

Rupture of large arteries and “hollow” organs

Life-threatening form of EDS.

Question 22

Collegen Disease: Ehlers Danlos Syndrome (Classical)

Answer 22

Type V Collagen Mutation

• Autosomal dominant (often de novo mutation)
• COL5A1 or COL5A2 genes
• Joint hypermobility and hyperensemble skin

Symptoms:

• Easy bruising
• thin & wide scars (cigarette paper scars)

Question 23

Collegen Disease: Ehlers Danlos Syndrome (Vascular)

Answer 23

Type III Collagen Mutation

• Autosomal dominant: COL3A1 gene (type III collagen)
• Effects: Skin, blood vessels

Symptoms:

• Thin skin, easy bruising
• Rupture of large arteries and “hollow” organs = Life-threatening form of EDS.

Question 24

Menkes Disease

Answer 24

X-linked recessive: Mutation in the ATP7A gene

• ATPase = intestinal copper uptake & transport
• Impaired copper absorption = deficiency = ↓ Lysyl Oxidase activity

Symptoms

• parse, brittle (‘kinky”) hair
• Low body temperature
• CNS features: hypotonia and seizures
• Poor growth and developmental delay
• Osteoporosis/fractures
• Usually fatal in childhood

Contrast with Wilson’s disease = copper excess due to defects in ATP7B gene)

Question 25

Scurvy

Answer 25

_Vitamin C Deficiency_ * Vitamin C is **required for hydroxylation of proline and lysine** * Scurvy = brittle collagen * via **defective pro-α-chains that NO form triple helix** * Degraded in cell (not secreted) Symptoms: * Fragile blood vessels (bleeding/bruising) * Loss of teeth * Loss of wound healing

Question 26

Aging Wrinkles

Answer 26

* **↓↓↓↓↓↓ of *_elastin*_ and _*collagen_*** in dermis * Also collagen/elastin **fibers thicken and clump**

Question 27

Scleroderma (Systemic Sclerosis)

Answer 27

_Autoimmune_ disorder Caused by **fibroblast activation = ↑↑↑ collagen deposition** * Stiff, **hardened tissue (sclerosis)** * Skin, other organ systems involved

Question 28

Defects in Lysosome **Collagen Recycling**

Answer 28

**collagenase**: first partially breaks down old collagen * The broken collogens are _phagocytosed and degraded_ by ***_lysosomal_*** enzymes several disease via exs ↑↑↑ collagen degradation 1. **Rheumatoid arthriti**s: too much degradation of cartilage collagen 2. **Osteoporosis**: similar but with bone collagen

Question 29

Intro to Elastic Fibers

Answer 29

**\>\>\>\> flexible** _than collagen_ * **Made by fibroblast**s, also smooth muscle cells, endothelial cells, and chondrocytes (cartilage cells). * **Interwoven with collagen** in mesh pattern to form a three-dimensional network. * **Prevent tearing from excessive stretching** * Present in skin, lungs, ligaments, vocal cords, spinal ligaments and especially arteries

Question 30

Elastin

Answer 30

* **ELN gene** makes the **Elastin** of elastic fibers (stretching/recoil) * Secreted as ***_tropoelastin_*** * Assembled into elastin fibers with **crosslinking via desmosine** * Contains **glycine, lysine, and proline** (*like collage*n) * **Mostly non-hydroxylated AA** * _NO HYDroxy LYSine_ * some HYDroxyPROline * **NOT** **glycosylated**

Question 31

"the scaffold" for elastin: **Fibrillin** microfibrils

Answer 31

**Fibrillin-1** = A glycoprotein the forms **head-to-tail polymer fiber** 1. **Tropoelasin binds** and forms a **bundle**. 2. *_Lyslyl oxidase_* make cross-links to make mature fiber 3. **On _outside of elastin_ fibers**

Question 32

Elastin Disease: Emphysema

Answer 32

Autosomal **co-dominant disease of α1-Antitrypsin (AAT)** * **Imbalance** between **elastase** (**destroys** **elastin**) and elastase **inhibitor AAT (protects elastin)** * **elastase** breaks down Elastin * Elastase activity is is *_stopped_* by **enzyme** **AAT** _Mutation= exs ↑ elastin DEGRADATION_ * AAT = **misfold & aggregate** in RER of **hepatocytes → ↓↓↓ AAT secretion = ↑↑↑ Excessive breakdown of elastin** * Emphysema = Lung damage * Common in Cacasians of Northern European ancestry

Question 33

Williams Syndrome or **Williams-Beuren Syndrome**

Answer 33

Partial **deletion** of long arm **of chromosome 7** (includes gene for **elastin**) Symptoms: 1. Elfin appearance 2. intellectual disability 3. **Supravalvular** aortic stenosis (narrowing) * poor construction of **ascending aorta** above (aortic valve) * **High prevalence among children** with WS * Histology: Loss of elastin

Question 34

Marfan Syndrome

Answer 34

Genetic Disorder of CT (Fibrillin) * Mutations in **FBN1 gene (chromosome 15)** that codes for fibrillin-1 = Abnormal fibrillin Symptoms * Classic appearance: **Tall** with long wingspan, Pectus **Excavatum** (**sunken** **chest**) * Extremities: **Hypermobile** joints, **long fingers** & toes. * **early** onset **Cataracts** and **dislocation** of **lens**.

Question 35

Adhesive Proteins

Answer 35

**Glycoproteins** that **join** and organize the ECM and **link cells to the ECM** 1. **Fibronectin** is the adhesive protein in **connective** tissues. 2. **Laminin** is the principal adhesive protein in **epithelial** tissues. _fibronectin_ or _laminin_ LINK **proteoglycans** and **collagen** to each other + to a cell's surface

Question 36

Keratin

Answer 36

* _homologous_ _protein_ with filamentous **(fibrous) structure** * expressed in epithelial cells and in epidermal derivatives such as **hair, nail, and horn.** * **α-keratin** : polypeptide chain, typically high in **alanine, leucine, arginine,** and cysteine, that forms a **right-handed α-helix.** * *_Stabilized_* by **hydrogen** and **disulfide** **bonds**.

Question 37

Fibronectin

Answer 37

* composed of a **dimer** linked by **disulfide bond**s near their C-termini (**V shape**) * **Attaches** cells **to all** matrices EXCEPT type IV (_laminin_) * Multimodular structure composed of FN-I, FN-II, and FN-III. * The primary sequence of _fibronectin connected to integrin_ is a tripeptide ***_Arg-Gly-Asp_*.**

Question 38

Basement Membrane & Laminin

Answer 38

## Footnote laminin molecules self-assemble & form networks that **bind to T_ype IV collagen_** Its **globule** **domains** bind with _ECM_ & cell surface _receptors_, thus linking cells = **Basement Membrane** (right below ECM)

Question 39

Laminin

Answer 39

* composed of **three** **chains** (α, β, γ) arranged in the shape of an **asymmetrical cross** (merosin) * **coiled-coil domains** joing the 3 chains into the cross heterotrimeric structure called **merosin**.

Question 40

Defects in Laminin

Answer 40

1. Junctional **epidermolysis** **bullosa** (**JEB**) = defects in **Laminin 5 OR 6** 2. **Epidermolysis**: rare diseases that cause **fragile**, **blistering** **skin** by even minor injury

Question 41

Structure of α- Keratin in Hair

Answer 41