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Biochemistry > Fibrous Proteins > Flashcards

Fibrous Proteins Flashcards

1
Q

Collagen is synthesized majorly by

A

fibroblasts

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2
Q

collage can also be synthesized by

A

muscle cells and epithelium

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3
Q

Most common type of collagen

A

Type I Collagen

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4
Q

Type I collagen chains

A
  • two alpha1 chains
  • 1 alpha2 chain
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5
Q

Type II collagen chains

A
  • three alpha1 chains
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6
Q

Type I collagen Location

A
  • ECM
  • Loose connective tissie
  • bone
  • tendons
  • skin
  • cornea
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7
Q

Describe a typical collagen molecule

A
  • long, rigid structure
  • three alpha- chains intertwined one to another
  • rope- like triple helix Qry structure
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8
Q

Type II collagen location

A

cartilage, vitreous humour

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9
Q

Type III Collagen Location

A

Are really reticular fibers and have diverse distribution

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10
Q

Type IV collagen location

A

Basement membrane or basal lamina

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11
Q

All collagens have 3 polypeptide chains with at least…

A

one stretch of triple helix

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12
Q

Non- triple helical domains of collagen

A
  • non- collagenous domains
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13
Q

Type IV collagen non- collagenous domain

A
  • Found at Carboxy terminus
  • called as NC1 domain
  • forms a mesh- like structure because its large
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14
Q

Alport Syndrome

A
  • Mutations to the genes coding for Type IV collagen
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15
Q

Goodpasture’s Syndrome (autoimmune)

A
  • antibodies against the alpha 3 protein constituent of Type IV collagen
  • attacks the basement membranes of
    • glomeruli
    • alveoli
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16
Q

Collagen Structure

A
  • Rich in Pro and Gly
  • Repeats: Gly- X- Y
    • X= any amino acid
    • Y= Proline or Hydroxyproline
  • 3 alpha chains
    • each in a non- classic alpha- helix conformation
  • Contains post- translational derivatives of Pro and Lys
    • Hydroxyproline (Hyp)
    • Hydroxylysine (Hyl)
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17
Q

Biosynthesis of collagen: Pre- pro alpha- chains

A
  • prepro-a- chains contain a signal sequence at the N- terminus that targets the polypeptide into the lumen of the rER
  • signal sequence is cleaved in the rER to yield a pro- a- chain
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18
Q

Biosynthesis of collagen: pro-a- chain in the rER

A
  • Random selection of Pro and Lys residues contained in the pro-a- chain undergo hydroxylation
  • after hydroxylation …
    • Selected Hydroxylysine residues are glycosylated with glucose and galactose
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19
Q

Hydroxylation of Pro and Lys residues at the rER

A
  • coenzyme: ascorbic acid (Vit C)
  • prolyl hydroxylase: makes Hyp
  • lysil hydroxylase: makes Hyl
20
Q

Biosynthesis of collagen:

Begining of the formation of pro- collagen triple helical molecule

A
  • Interchain disulfide bridge formation between 3 pro- alpha- chains
  • Hydrogen bonds stbilize the triple helical conformation of pro- collagen
21
Q

Biosynthesis of collagen:

Translocation of procollagen and secretion

A
  • molecule translocates to Golgi
  • is packaged into vesicles
  • vesicles fuse with the plasma membrane
  • secreted into the ECM
22
Q

Biosynthesis of collagen: Procollagen clipping at the ECM to yield tropocollagen

A
  • procollagen molecules are clipped
  • C and N- terminal propeptidases
  • Now is called tropocollagen
23
Q

Biosynthesis of collagen:

Tropocollagen maturation to yield mature collagen

A
  • Lysyl oxydase
    1. aldol condensation
    2. Schiff base formation
  • mature collagen is obtained
24
Q

ECM Lysyl Oxydase

A
  • Copper requiring enzyme
  • catalysis of tropocollagen into mature collagen
  • performs
    • aldol condensation
    • Schiff base
  • covalent cross- linking of collagen molecules
25
Q
A
26
Q

Summary of Biosynthesis of Collagen

A
  • RER synthesis pre-pro-α-chain with signal sequence .
  • Pre-pro-α-chain enters into lumen of RER where signal sequence is clipped (pro-α-chain), proline and lysine hydroxylation occurs.
  • S-S bond formation between the pro-α-chains (initiates the winding process) to produce procollagen .
  • Procollagen moves to Golgi (processing of oligosacharide chains)
  • Procollagen loaded into vesicles and are secreted into ECM
  • Propetidases cleave N- and C-terminal propetides convert procollagen to tropocollagen.
  • Tropocollagen undergo cross-linking to form mature collagen.
27
Q

4 diseases of abnormal collagen synthesis

A
  1. Osteogenesis Imperfecta
  2. Ehlers- Danlos Syndrome
  3. Menke’s Syndrome
  4. Scurvy
28
Q

Describe Osteogenesis Imperfecta

aka “brittle bone disease” or “Lobstein syndrome”

A

Type I collagen affected

  • Mutations
    • COL1A1 : proa1 (I) chain gene
    • COL1A2: proa2 (I) chain gene
  • 90% : reduced synthesis of proa1 (I) chains
  • others involve single base subsitution
    • Gly—> bulky AA= compromise the structural integrity of the molecule
29
Q

Osteogenesis imperfecta: Clinical

A
  • Osteopenia—-> brittle of bone
  • “pop-corn like” deposits of mineral in x- rays of the long bones is an ominous sign (bad indicating)
  • frequently Blue Sclera
  • Dentinogenesis imperfecta
    • due to lacking dentin
  • progressive hear loss
  • positive familial history
30
Q

Ehlers- Danlos Syndrome (EDS)

A
  • different types of EDS
  • typically affects the joints, skin and blood vessels
  • characterized by
    • hypermobile joints
    • hypereslasticity of the skin
31
Q

Classic EDS I -severe

A
  • Affected: Collagen Type V
  • Mutations:
    • COL5A1
    • COL5A2
32
Q

Classic EDS II: Mild

A
  • Affected: Collagen Type I
  • Mutations:
    • COL1A1
    • COL1A2
33
Q

EDS III: Hypermobile EDS

A
  • Affected: Tenascin X.
    • minor component of the CT that appears to regulate the assembly of collagen fibers
  • Mutation:
    • TNXB gene
34
Q

EDS IV: Vascular EDS

A
  • Affected: Collagen Type III
  • mutation:
    • COL3A1
35
Q

Ehlers- Danlos Syndrome Signs and symptoms

A
  • Ligament and Joint changes
    • laxity and hypermobility of joints
    • mild to irreducible dislocation of hips and other large joints
  • Skin (variable)
    • thin
    • velvety
    • hyperextensibility “rubber person syndrome”
    • cigarette- paper scars
  • Easy bruise
  • mitral valve prolapse and hernias
  • scoliosis
  • degenerative arth
36
Q

Scurvy

A
  • Deficiency in ascorbic acid (Vitamin C)
    • required for the proper functioning of key hidroxilating enzymes:
      • prolyl hydroxylase
      • lysyl hydroxylase
    • No stabilization of the procollagen structure
    • impaired fibrillogenesis
37
Q

Scurvy Signs and symptoms

A
  • BLEEDING
  • Skin changes with roughness
  • Corkscrew hair
  • petechiae
  • easy bruising
  • loosening of teeth
  • poor wound healing
38
Q

Menkes Disease

A
  • X- linked genetic disease
  • Mutation
    • ATP7A
      • deffective copper binding P- type ATPase
  • Decreased activity of copper (Cu) dependent Lysyl oxidase
    • defective collage cross- linking
39
Q

Menkes Disease Signs and Symptoms

A
  • Low serum Cu levels
  • Deposition of Cu in intestinal cells
  • Brittle hair
  • growth failure
  • deterioration of the nervous system
40
Q

Elastin fibers

A
  • integrity of CT
  • found abundant in
    • aorta
    • ligaments
    • ciliary nodules of the eye
  • distensible property
41
Q

Elastin: Biological features

A
  • Precursor: Tropoelastin secreted into the ECM
  • Lysil oxidase: Lys contained in tropoelastin is converted into allysine
  • 3 allysines and 1 unmodified Lys react to form desmosine
  • desmosine cross-liking yields elastin (extensively interconnected)
42
Q

a1- antitrypsin

A
  • Function: protects elastic tissues of the lung from destructive action of elactases.
  • Inherited deficiency:
    • emphysema
    • cirrhosis
  • Positive acute phase protein
43
Q

Elastin and a1- antitrypsin

A

a1- antitrypsin protects elastin from being degraded by inhibiting the neutrophil elastase

*Neutrophil elastase: degrades elastin of alveolar walls and other tissue proteins

44
Q

a1- antitrypsin: biological features

A
  • inhibits a number of proteolytic enzymes including elastases
  • synthesis
    • mainly: liver
    • other: monocytes and macrophages
  • Mutation: a1-AT gene
    • Substitution: (GAG- AGG)
      • Lys— > Glu
  • mutated protein
    • polymerized in the rER of hepatocytes, not secreted
45
Q

a1- Antitrypsin (A1AT) deficiency

A
  • autosomal RECESSIVE
  • decreased function A1T1 in:
    • Blood
    • lungs
  • increased deposition of abnormal A1T1:
    • liver
      • impairing liver function
        • possible cirrhosis and failure
  • Severe deficiency => panacinar emphysema (COPD)
    • specially if exposed to cigarette smoke
  • Symptoms:
    • SOB
    • wheezing
    • rhonchi
46
Q

Marfan’s Syndrome

A
  • Autosomal dominant
  • Mutation: FBN1
    • glycoprotein ​Fibrillin- 1
      • biogenesis and maintenance of elastic fibers
  • Problem:
    • Affected Fibrillin-1 binds a latent form of TGFß keeping it sequestered
      • inability to do function
    • Reduced levels of fibrillin-1 affectinng normal function of elastin
    • TGFß levels increase also inappropiate for the ECM
47
Q

Marfan’s syndrome: Clinical presentation

A
  • Triad:
    • long limbs
    • dislocated lenses
    • aortic root dilatation
  • Skeletal:
    • Arachnodactyly
    • scoliosis
    • pectus excavatum/ carinatum
    • joint flexibility
    • stretch marks
  • Cardiac
    • Prolapse of the mitral/ aortic valves (and signs of regurgitation)
      • Signs: Cold limbs
    • palpitations
    • angina pectoris
  • Lung: risk of spontaneous pneumothorax

Biochemistry (7 decks)

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