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128 Cards in this Set
- Front
- Back
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Name the connective tissues found in the body:
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Cartilage
Bone Tendons, ligaments Sub-epithelial layers (basal lamina, dermis) |
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What are the 3 major classes of macromolecules in connective tissue?
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1. Proteins
2. Glycosaminoglycans (GAGs) 3. Proteoglycans |
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What are the 2 main categories of ECM Proteins? Give 2 examples of each.
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-Structural - collagens, reticulin, and elastins.
-Cell binding - laminins and fibronectin |
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What are the 4 GAGs (Glycosaminoglycans)?
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-Hyaluronans
-Chondroitin sulfates -Heparin sulfates -Keratan sulfates |
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What are proteoglycans?
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Proteins with GAGs bound to them.
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What proteoglycan is found in cartilage?
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Aggrecan
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3 types of Structural Proteins in ECM (again)
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1. Collagen
2. Reticular fibers 3. Elastic fibers |
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What are reticular fibers?
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Fibers that form a reticulum network made up from the same protein subunits as COLLAGEN.
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How is reticulin different from collagen?
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-Its fibers are thinner
-Network instead of aligned -Resists forces from various directions. |
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What tissue are reticulin fibers important for stabilizing?
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Small blood vessels and nerve twigs.
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What is the name for the interwoven network of reticulin?
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Stroma
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What is the function of stroma?
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Stabilization of parenchyma (functional cells).
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What protein composes Elastic fibers?
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Elastin
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What is the structure of elastic fibers like?
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Single wavy elastin molecules are cross-linked to form network that expands/contracts randomly.
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How are elastin molecules held together?
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Via covalent bonds.
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Where are elastin fibers functionally important?
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In joining vertebrae
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What are 2 types of CELL BINDING PROTEINS in connective tissue?
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1. Fibronectins
2. Laminins |
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How much protein in the body is collagen?
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25% by mass
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What are the 4 common structural elements of collagen?
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1. Made of a trimer helix
2. Rich in hydroxy/proline and hydroxy/lysine 3. Glycine is the AA at every 3rd residue 4. Its native structure is a trimer |
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How can the collagen trimers be made up?
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As homotrimers or heterotrimers
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How many different gene products of collagens exist?
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At least 33!!!
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What is the collagen superfamily arrangement like?
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There are 27 collagen types arranged in 7 classes.
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What is Procollagen?
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A trimeric protein secreted from cells
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What is the structure of procollagen composed of?
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Central: triple helical domain
Ends: globular amino- & carboxy-terminal ends (propeptides). |
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What is tropocollagen?
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Aka, Collagen. What remains when propeptides (ends) of procollagen are removed.
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What is the tropocollagen structure composed of?
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Triple helix of 3 polypeptide subunits, supercoiled.
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What is at the ends of the tropocollagen?
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Telopeptides - these are involved in microfibril formation.
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What is a collagen microfibril?
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The precursor to collagen fibrils.
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How do microfibrils assemble?
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By self-assembly of tropocollagens into a staggared arrangement
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What is the self-assembly of tropocollagens into microfibrils called?
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Concatenization - head to tail w/ intervening 35 nm gap, side-side in staggard arrangement.
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What does the staggard arrangement of tropocollagens achieve?
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Greater stability as the electrostatic and hydrophobic interactions are maximized.
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How is microfibril structure stability achieved?
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Via covalent cross-linkages btwn tropocollagens.
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What does the crosslinking of tropocollagens involve (chemically)?
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Oxidative deamination of lysine and hydroxylysine!!
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Give the actual structure of:
-Primary structure -2ndary structure -Quaternary structure |
1' = x-y-Gly
2' = left-hand helix 4' = right-hand superhelix |
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Describe the 2ndary helical structure of collagen
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-right handed
-3 AA per turn -Every 3rd residue is Gly |
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Why is every 3rd residue gly in collagen?
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Because Gly is the only residue that accomodates the unique left-hand superhelix conformation it assumes.
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What type of characteristic does Collagen show on a Ramachandran plot?
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Very tight, narrow area - b/c the Psi/Phi angles of the primary structure occupy a vary narrow range.
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What are the 2 main areas of collagen synthesis and assembly?
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1. Intracellular
2. Extracellular |
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What 3 things are accomplished during the intracellular phase?
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1. Form single-strand helix
2. Hydroxylate/glycosylate AA's 3. Assemble triplex |
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What are the 4 things accomplished in the extracellular phase of collagen synthesis?
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1. Cleave terminal propeptides
2. Assemble multiple collagens into a fibril 3. Covalently crosslink fibrils 4. Aggregate fibrils -> fibers |
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What is Step 1 of intracellular processing?
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Hydroxylation of Proline
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What are the requirements for proline hydroxylation?
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-Ascorbate
-alpha-ketoglutarate -Oxygen -Fe2+ |
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What enzyme achieves proline hydroxylation?
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Prolyl hydroxylase
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What is the actual proline hydroxylation reaction?
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A dioxygenase reaction with 2 components:
1. Oxydative decarboxylation of alpha-ketoglutarate 2. Hydroxylation of proline |
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Why is ascorbate essential for collagen formation?
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IT keeps the enzyme's Fe2+ in the reduced state.
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What happens when ascorbate is not available?
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Fe2+ is oxidized to Fe3+ and the enzyme is incapable of hydroxylating proline.
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What happens when proline is not hydroxylated?
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Collagen is much less stable and has a reduced melting temp
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What is the Tm of collagen?
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The temp at which half the proteins are unfolded.
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What is a potential way to control excessive collagen synthesis?
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Use inhibitors of prolyl 4-hydroxylase to inhibit synthesis.
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What are the pluses/minuses of using Prolyl hydroxylase inhibitors?
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Pluses: collagen specific; collagen proteins will melt at biological temp (37)
Minuses: ALL collagens unstable; accumulation and reintroduction of the enzyme causes 'crisis' of functional collagen - lifelong therapy. |
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What is the 2nd intracellular processing step?
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Hydroxylation of Lysine.
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How does lysine hydroxylation proceed?
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Same manner/requirements as Proline hydroxylation.
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What is the function of hydroxylated lysine?
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-substrate for glycosylation
-Crosslinking |
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What is the function of hydroxylated proline again?
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Increasing the Tm of collagen (stability).
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Which positions in collagen's AA chain are held by Lys/Pro?
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Gly = glycine
X - lysine Y - Proline |
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In what cell compartment does lys/pro hydroxylation occur?
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Both in the endoplasm. reticulum.
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During post-translational modifications what else happens other than Pro/Lys hydroxylation?
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O/N-glycosylation
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Where does glycosylation occur?
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-N glycosylation in ER
-O glycosylation in Golgi |
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What does N-glycosylation consist of?
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Glycosylation of N atom on Asparagine side chains
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What does O-glycosylation consist of?
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Glycosylation of Hydroxyl groups (Ser/Thr)
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How is O-glycosylation of Collagen specifically done?
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Addition of Glucose/Galactose to Hydroxylysine residues.
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Why does collagen get glycosylated?
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Because the sugars are involved in crosslinking collagen fibers.
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What is step 3 of collagen intracellular processing?
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Initiation of triple superhelix formation at the C-terminal propeptides.
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What is the significance of the C-terminus in the collagen protein structure that allows the triple helix formation to begin?
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It is rich in Cysteine residues.
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What stabilizes the three collagen chains as superhelix formation begins?
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Disulfide bonds between the 3 molecules.
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What is step 3 in collagen intracellular processing?
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Zipping up the triple helix structure.
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What direction does collagen zipping up go?
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C-terminus -> N-terminus
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What is the rate-limiting step in collagen synthesis?
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Cis-trans isomerization of proline residues.
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Which step is proline isomerization?
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Step 5
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Why must proline be isomerized?
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Because it is the one AA residue that can exist in both cis and trans isomers.
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What enzyme is responsible for catalyzing cis-trans isomerization of proline?
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Prolyl isomerase
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What is the 6th step in intracellular processing of collagen?
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Hydrogen bonding between chains to stabilize triple helix.
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Where do the H bonds occur in step 6?
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Between Glycine residue Hydrogens, and C=O groups on adjacent chains.
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What is step 7 of intracellular processing?
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Exocytosis of the protocollagen molecule from the cell.
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What does protocollagen consist of?
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Core triple helix, N- and C-terminal propeptides.
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What is the first step in extracellular processing of collagen?
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Proteolytic cleave of N/C-terminal propeptides
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What enzyme cleaves the propeptides?
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Procollagen proteases - one specific for N and C-termini.
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What results from the cleavage of procollagen?
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Tropocollagen (mature).
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What is step 2 of extracellular processing of tropocollagen?
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Self-assembly into a protofibril.
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What is the structure of a collagen protofibril like?
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Head-to-tail, side-by-side lateral associations of helices that are staggared.
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What is step 3 in extracell. processing?
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Crosslinking of neighboring fibers.
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How is protofibril crosslinking achieved?
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By the covalent crosslinking of neighboring lysines/hydroxylines.
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What is the first step in lysine crosslinking?
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Converting the lysine residues to aldol form - allysine or hydroxyllysine.
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What enzyme catalyzes lysine aldol formation?
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Lysyl oxidase
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What occurs after the initiation of lysine crosslinking?
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Aldol condensation in one of 2 alternate methods.
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What is the first type of lysine crosslink?
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Aldol condensation of 2 neighboring allysines.
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What is the 2nd type of lysine crosslinking?
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Crosslinkage of Allysine and neighboring Lysine; then amadori rearrangement.
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What occurs after lysine crosslinkage of mature collagen?
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Aggregation of fibrils to form fibers.
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What type of staining pattern do collagen fibers exhibit?
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Dark and light striated patterns.
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What are 3 types of collagen diseases in general?
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1. Inherited
2. Dietary 3. Autoimmune |
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What are the 2 important human diseases associated with Collagen type 1?
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-OI = Osteogenesis imperfecta
-ED = Ehlers-Danlos |
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What type of inheritance pattern is assoc. w/ OI?
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Autosomal dominant
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What are the main pathologic characteristics of OI?
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-Abnormal Type 1 Collagen
-Brittle bones -Repeated fractures at minor trauma sites. |
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What are the main differences between OI type 1 and 2?
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Type 1 = most common, mildest. Fractures easily. Sclera blue; teeth/ossicles deformed. Collagen structure is NORMAL but decreased amt.
Type 2 = most severe, lethal at/shortly after birth. Improper collagen structure. |
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How specifically is collagen synthesis different in Types 1 and 2 OI?
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Type 1: normal collagen, decreased amts.
Type 2: abnormal collagen. |
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What type of mutation is seen in OI types 1 and 2?
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Type 1: null mutation in one copy of alpha-1 gene.
Type 2: subtle mutation in same. |
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How many alpha-1 chains must be mutated to result in non-functional collagen?
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Even one is sufficient!
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What is the functional result of Type 1 OI mutation?
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only 50% of normal collagen produced.
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What is the functional result of Type 2 OI mutation?
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Only 25% of normal collagen produced, 75% of abnormal (nonfunctional) produced.
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What dietary insufficiency results in collagen deficiency?
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Scurvy - ascorbate (vit C) deficiency
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What autoimmune disease is associated with collagen abnormality?
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Bullous Pemphigoid
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What is the molecular basis of bullous pemphigoid?
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An autoantibody is produced against BP180; Complement is activated, Neutrophils called, Protease sereted, and Adhesion molecules cleaved.
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What is the result of cleaving adhesion molecules in bullous pemphigoid?
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Basal cells are detached from the dermis.
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Review; the types of ECM tissue are:
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-Proteins
-GAGs -Proteoglycans |
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2 categories of protein:
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1. Cell binding
2. Structural |
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2 types of cell binding proteins:
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1. Fibronectin
2. Laminectin |
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What is the structure of fibronectin like?
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-Dimeric w/ intersubunit disulfide bonds.
-6 domains (5 are binding sites for other proteins) |
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What component of fibronectin is the binding site for integrin?
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The RGD loop
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Describe the integrin-binding subunit of Fibronectin:
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-7 beta sheets
-Antiparallel composition -Disordered loop is the actual binding site. |
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What are laminins?
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Another type of cell-binding protein
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What type of structure do laminins have?
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Hetero-trimer composed of alpha, beta, gamma chains.
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What is the function of laminin?
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To serve as binding sites for other matrix molecules.
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What are the 3 types of structural proteins?
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1. Collagen
2. Reticular fibers 3. Elastic fibers |
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What are 3 general features of collagen to remember?
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1. Long, straight, unbranched.
2. Most common fiber in connective tissue. 3. Semi rigid rods |
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What is reticular fiber made of?
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Same protein as in collagen.
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How is reticular fiber different from collagen?
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-Subunit arrangement and interactions are different.
-Tough but flexible -Branches |
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What is the main function of reticular fiber?
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Stabilization of organ vasculatures.
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What are elastic fibers?
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Branched, wavy fibers made of the protein elastin which serve functions like vertebral interconnection.
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What are GAGs?
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Glycosaminoglycans.
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What are GAG structures like?
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Long, unbranched chains of repeating disaccharides that undergo subsequent modifications like sulfate addition.
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What is the non-sulfated GAG?
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Hyaluronic acid
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What are the sulfated GAGs?
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-Chondroitin Sulfate
-Dermatan sulfate -Herparan sulfate -Keratan sulfate |
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What is the purpose of GAGs?
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To attach to a core proteoglycan
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How do GAGs attach to proteoglycans?
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Via covalent links through O-glycosidic bonds, to Ser residues on the core protein.
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Why do proteoglycans resemble bottle brushes?
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Because the GAG's extend out and repel each other via charge repulsion.
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Which GAG associates with proteoglycans?
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Hyaluronic acid
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What stabilizes GAG-proteoglycan assemblies?
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link proteins
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What is the sugar:protein ratio in proteoglycans?
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Much greater than 1
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