Fibrillar Proteins

Question 1

Compare globular and fibrillar proteins based on

Shape

variation of secondary structure

molecular weight

water solubility

roles

Answer 1

• Globular=sphere, fibrillar= rod
• Variety of secondary structure/repeating
• Variable/high
• High/low
• functional/dynamic vs structural

Question 2

Collagens

How much of human protein?

Where located?

Abnormal collagen synthesis or structure causes problems with…

Amino acid composition and needed enzymes

Why are these AA frequent?

Typical AA repeats

Answer 2

• 25% of all protein (most abundant)
• everywhere (most of bone, not much of liver)
• cardiovascular organs (aneurysms, heart valve malfunctions), bone (fragile, fracture), skin (poor healing, hyper-extend), joints (hypermobile, arthritis), eyes (lens dislocation)
• 33% Gly, 13% Pro, 9% OH-Pro, some OH-Lys (need Pro hydroxylase and Lys hydroxylase and vitamin C)
• Gly is small, fit into small places, Pro prevents alpha helix, Hydroxyl groups allow crosslinks, OH-Lys can be glycosylated
• Gly-Pro-Y, Gly-X-Hyp

Question 3

Collagen secondary structure

Collagen tertiary structure

Fibril formation- how it occurs and why important?

What is staining pattern of collagen fibrils?

How are crosslinks formed in collagen?

Answer 3

• polyproline type II helix (left-handed, 3 residues/turn), plane of each peptide bond perpendicular to helix axis
• 3 member super-helix (right handed), interchain H-bonds w/ other collagen chains via OH-Pro
• Self-aggregated in quarter-staggered parallel arrays and become covalently cross-linked (needed for structual strength or form a meshwork w/ filtering capacity)
• Alternate light/dark where there is no gap/gap
• Amino group of Lys side chain converted to aldehyde to form allysine (lysyl amino oxidase + Cu), then spontaneously reacts w/ normal Lys to form covalent bond linking superhelices

Question 4

Collagen Type I synthesis

How much of each chain is formed?

What are post-translational modifications inside cell?

How does it leave cell?

What happens outside cell?

Answer 4

• 2 alpha1(I) chains and 1 alpha2(I) chain
• Hydroxylation of Pro and Lys, glycosylation. Also disulfide bonds, and cleave signal sequence (preprocollagen). Leads to triple helix formation
• Leaves cell as procollagen (propeptide doesn’t allow self-aggregate)
• Propeptides cleaved by procollagen peptidases, self-assemble into fibers, lysyl oxidase allows crosslinking of triple helices

Question 5

Collagen degradation

Are collagens stable?

What enzymes degrade collagen?

Answer 5

• Yes, very long half lives
• MMPs called collagenses hydrolyze them
• Also, gelatinases degrade them further after triple helix unwinds

Question 6

Collagen disorders

What do we need for normal collagen formation?

Abnormal collagens arise from…

Scurvy (who is at risk today, symptoms, clinical problems)

Answer 6

• Activation of appropriate genes, Gly/Pro in right spot, hydroxylation of Pro/Lys (enzyme/vitamin C), Glycosylation of OH-Lys (enzyme), removal of propeptides (enzymes), crosslinking of triple helices (correct AA, enzyme, Cu)
• Genetic defects in collagen genes, abnormal posttranslational modification (genetic defects in modifying enzymes, cofactor deficiency)
• Lack of Vitamin C (only issue in infants who get formula fed), suppress growth of bone in kids, hemorrhage, poor wound healing, less procollagen synthesis, joint damage, orthopedic problems

Question 7

Osteogenesis Imperfecta overview

OI common symptoms

MORE

Answer 7

• “brittle bone disease”, mutation in alpha I or II genes for type I collagen lead to aberrant alpha chains, unstable helices cannot enter ER.
• Have multiple fractures, bone deformities, progressive deafness, defective dentition, blue sclera

Question 8

Ehlers-Danlos Syndrome common symptoms

Type IV (pattern, mutation, symptoms)

Type VI

Type VII

Type IX

Answer 8

• Weakened connective tissue (thin, fragile skin, impaired joints, hyperextensive skin, hypermobile joints)
• Autosomal dominant, deficient type III collagen, think skin/ruptured arteries and internal viscera (dangerous to get pregnant b/c of this)
• Autosomal recessive, no lysyl hydroxylase. Get scoliosis, velvet skin, hypermobile joints, ocular injuries
• Autosomal dominant, can’t remove N-terminal propeptide. Get hypermobile joins, joint dislocations, soft skin
• X-linked recessive, deficient in lysyl oxidase so less crosslinking (or Cu deficient due to diet, defect in Cu transport, distribution, or Cu-chelating drug). Hyperextensive skin, bladder diverticulae, skeletal deformities

Question 9

Elastin

Function

Where abundant

Shape and water solubilitiy

AA composition

Answer 9

• Elasticity in tissues
• ligaments, lungs, arterial walls, skin
• fibrous, insoluble in water
• apolar amino acids

Question 10

Elastin Structure

Modified residues?

Elastin degradation enzyme, inhibitor

How do you get emphysema?

Answer 10

• Unordered coiled strucutre, AA residues highly mobile
• Modified Lys residues (allysines) by lysyl amino oxidase, desmosine and isodesmosine also
• Elastase- serine proteinase specific for apolar AA, inhibited by alpha-1-antitrypsin to avoid tissue damage
• When elastase inhibitor is decreased in conc. of damage by smoking

Question 11

Microfilament

Actin (monomer, polymer, action)

Myosin (monomer, polymer, action)

Functions

Answer 11

• G-actin gobular, F-actin fibrillar, polymerization/depolymerization
• fibrillar -head +coiled-coil tail, fibrillar bundle filament, motor protein for actin which transduces ATP energy to mechanical work
• Cell shape, locomotion, signaling, cell/cell contact, endocytosis

Question 12

Microtubules

Monomer/Polymer/Action

Associated dynamic proteins

functions

+/- ends

Colchicine

Taxol

Alzheimer’s and microtubules

Answer 12

• globular, alpha/beta-tubulin; fibrillar, hollow tubular network;polymerize/depolymerize
• dynein and kinesin, transduce ATP energy to mechanical work
• change in cell shape in response to external signals, reinforce cytosol elements, construct cilia/flagella, mitosis (mitotic spindle), separate chromosome pairs, distribute organelles
• Grow at + ends (point towards cell periphery), microtubule organizing center (MTOC) at minus end
• disassemble microtubules, inhibits action of WBC to mediate inflammation by precipitation of uric acid in joints
• blocks cell division by binding to beta-tubulin subunits and stabilizing microtubules
• Abnormal tau protein can’t support microtubule assembly (inhibits polymerization)

Question 13

Kinesin vs dynein

Moves cargo towards

Structure

Energy used

Transports what?

Answer 13

• Kinesin= + end (Anterograde), dynein= - end (retrograde)
• Both: similar to myosin, 2 heads bind microtubule and tail; opposite end binds vesicle transported
• Both use ATP
• Kinesin= organelles, newly made molecules; Dynein= defective organelles, endocytosed molecules

Question 14

Intermediate filaments

Function

Polarized? Associated proteins?

Keratin (soft/hard)

Monomer/dimer/polymer

Skin keratin function

Keratin gene mutations

Hair keratin (where is strength from, can be stretched?)

Hair modifications (Straigtening, curling)

Answer 14

• Structural only
• No, rarely
• define internal body structures, strength for nuclear envelope/cells; build skin/hair/claws
• Coiled coils (dimer of 2 alpha-helices), 2 monomers assemble in anti-parallel fashion (protofilament), assemble to multimers and stabilize by disulfide bridge (filament)
• forms strong waterproof coating after skin cells die
• Epidermolysis bullosa simplex (EBS)- cells rupture from normal mechanical stress, visible separation of epidermal layers as blistering
• Multiple disulfide bonds give strength, can be stretched by force
• Reducing agents break disulfide bonds, oxidizing agents reform in different shape