CSB327 Lecture 4 Summary

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University of Toronto St. George
Cell and Systems Biology
Maurice Ringuette

CSB327 Lecture 4 Notes - Shaping of extracellular matrix by cells o Cells exert tractional (pulling) forces on adhesive ECM molecules o Integrin  Major class of cell-matrix transmembrane receptors that binds to ECM molecules such as collagen  Type I collagen can be recognized by a variety of different integrins  β1 is the common subunit in collagen receptors  Heterodimer derived from a combination of 18 α subunits and 8 β subunits  No enzymatic activity - Vectorial discharge by fibripositor o Fibril deposition into extracellular space o Movement of vacuoles to the cell surface for discharge results in their preferred localization to one region of the cell - Extracellular compartments o The interface between the cell surface and the matrix o First compartment  long narrow channel (fibril)  Elongated vacuoles fuse into long narrow fibril-forming compartments  Open to the extracellular space  Extend deep into the cell o Second compartment  fibril forming compartment (fibril bundles)  Retraction or lateral fusion of the plasma membranes of the first compartment  Form collagen fibril bundles  Manipulation of individual fibril segments is effected by interactions of the cell surface, traction and pulling forces  Likely mediated by matrix receptors such as integrins o Third compartment  fiber forming compartment (fiber)  Lateral aggregation of the plasma membranes of the second compartment  Form tissue-specific macroaggregates (fibers)  Tendon organization is uniaxial because the force is applied in one direction  Skin organization is biaxial (weave-like) because the force is applied in all directions - Heteropolymerism o Results from mixing different collagen species within a single fibril o Control fibril diameter during assembly  For example, type I and type V collagen is present as heterotypic fibrils  Type V collagen o Three transcriptional units o Switches isoforms during development o Regulates the diameter of type I collagen through the N-propeptide domain, which protrudes from the hole zone of type I collagen fibrils  EHLRS-DANLOS SYNDROME (EDS)  Classical type EDS  mutation of type I collagen and type V collagen o Affects intracellular or extracellular processing o Mutation in type I collagen (COL1A1 mutation)  Arg136Cys substitution mutation in α1(I) chain  Cys residue creates disulfide bonds between α-chains  Assembly of type I collagen fibrils with variable diameter and decreased tensile strength  SDS-PAGE gel of radiolabelled collagens  In EDS patient, there is an additional band corresponding to dimeric α1(I) chains  The dimer disappeared after reduction with β- mercaptoethanol  Suggests the presence of disulfide-bonded collagen α- chains o Mutation in type V collagen  Type V collagen co-localizes with type I collagen  Antibodies tagged with gold particles of different sizes enables researchers to differentiate between type I and type V collagen in the same TEM micrograph  Type V collagen is less abundant than type I collagen  Type V collagen co-polymerizes with type I collagen in vitro  The N-terminal domains stick out of the hole zone  Type V collagen regulates the initial rate of collagen fibrilloge
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