Cell Adhesions, cell-cell junctions and extracellular structures After completing this class you should be able to: • • • • • • • Understand how sliding motion of adjacent microtubules doublets is converted into the bending motion of cilia/flagella Understand how actin cross-linking and contractile properties of nonmuscle myosin II are regulated by Rho GTPases Know the major transmembrane proteins of tight and adherence junctions. Describe the functions of tight and adherence junctions. Know the different types of molecular complexes that mediate animal cell-cell interactions (desmosomes, adherens, gap and tight junctions) and their main functions Know the different types of molecular complexes that mediate animal cell-matrix interactions (hemidesmosomes, focal adhesions) Know the major transmembrane proteins desmosomes, adherens, gap and tight junctions Cilia and flagella are motile structures built from microtubules and associated proteins. The axoneme of motile cilia has a ring of nine outer microtubule doublets and two central singlets (called a 9+2 axoneme) SEM micrograph of the cilia projecting from respiratory epithelium in the lungs Doublet sliding within the axoneme causes cilia and flagella to bend Figure 16-83 Molecular Biology of the Cell (© Garland Science 2008) Major types of cell junctions Figure 19-3 Molecular Biology of the Cell (© Garland Science 2008) Major types of cell-cell junctions Figure 19-27 Molecular Biology of the Cell (© Garland Science 2008) Tight junctions in transmission and freezefracture electron micrograph Furuse et al., 2006 Four-transmembrane domain adhesion molecules claudins control paracellular transport Immunofluorescent staining of rat small intestine with anti-Claudin-1 antibody Tight Junctions control the passage of molecules and ions through the space between plasma membranes of adjacent cells, Tight Junctions help to maintain the polarity of cells by preventing the lateral diffusion of integral membrane proteins between the apical and lateral/basal surfaces Figure 10-37 Molecular Biology of the Cell (© Garland Science 2008) A Na+-glucose symporter and a glucose uniporter operate on opposite sides of epithelial cells to facilitate movement of glucose from the intestine to the blood. Figure 11-11 Molecular Biology of the Cell (© Garland Science 2008) Cell – cell anchoring junctions: desmosomes, and adherens junctions Figure 16-5 Molecular Biology of the Cell (© Garland Science 2008) Table 19-1 Molecular Biology of the Cell (© Garland Science 2008) Cadherins are transmembrane cellcell adhesion proteins At adherens junctions two adjoining cells are separated by a thin space of 20-25 nm Cadherin mediated cell-cell adhesion depends on calcium Like muscle sarcomeres, the NMII structures at the perijunctional actin belt are also contractile Figure 19-15 Molecular Biology of the Cell (© Garland Science 2008) Like muscle sarcomeres, the NMII sarcomeres at the perijunctional actin belt are also contractile Seham Ebrahim and Bechara Kachar., Cell Cycle. 2013 Periodic assemblies of bipolar NMII filaments, actin and αactinin form a continuous belt of muscle-like sarcomeric units (~400 – 600 nm) around epithelial cell. 3 μm Seham Ebrahim etal., Curr Biol 2013 The process of neural tube closure involves apical constriction Craniorachischisis Figure 19-16 Molecular Biology of the Cell (© Garland Science 2008) The two globular head domains of NM II contain a binding site for both ATP and actin This neck domain is followed by a long α-helical coiled coil, which forms an extended rod-shaped domain that effects dimerization between the heavy chains and terminates in a relatively short non-helical tai Figure 16-54a Molecular Biology of the Cell (© Garland Science 2008) Regulate NM II by making myosin heads unavailable for binding actin Non-muscle myosin II (NM II) is regulated by the phosphorylation of its light chains Miguel Vicente-Manzanares etal., Nat Rev Mol Cell Biol. 2009 Both smooth muscle and non-muscle myosin II are regulated by phosphorylation of the regulatory light chains. Small monomeric G proteins Rho-associated protein kinase (ROCK) phosphorylates myosin light chain (MLC) and MLC phosphatase Cell – cell anchoring junctions: desmosomes, and adherens junctions Figure 16-5 Molecular Biology of the Cell (© Garland Science 2008) Figure 19-27 Molecular Biology of the Cell (© Garland Science 2008) Cadherins are transmembrane cellcell adhesion proteins At adherens junctions two adjoining cells are separated by a thin space of 20-25 nm Cadherin mediated cell-cell adhesion depends on calcium Cadherin family proteins desmoglein and desmocollin are major cell-cell adhesion proteins in desmosomes Intermediate filaments play structural or tensionbearing role Figure 23-4 Molecular Biology of the Cell (© Garland Science 2008) At desmosomes two adjoining cells are separated by a thin space of 25-35 nm Desmosomes are one of the stronger cell-to-cell adhesion types and are found in tissue that experience intense mechanical stress Different types of transmembrane cell-cell adhesion proteins: CAM (cell adhesion molecule) Lectins - carbohydrate-binding proteins ICAM-1 (Intercellular Adhesion Molecule During an inflammatory response leukocytes move out of the circulatory system towards the site of tissue damage or infection. Leukocytes initiate attachment to the endothelial cell surface through the selectins, then stabilize the adhesion through the interaction between integrin and an ICAM ICAM-1 (Intercellular Adhesion Molecule 1) Major types of cell-cell junctions Figure 19-3 Molecular Biology of the Cell (© Garland Science 2008) Gap junctions directly connect the cytoplasm of two cells: connexons in the membrane of each cell are aligned with one another At gap junctions two adjoining cells are separated by a thin space of 2-3 nm Figure 19-35 Molecular Biology of the Cell (© Garland Science 2008) In vertebrates: connexons are hexamers of connexin transmembrane proteins Figure 19-34a Molecular Biology of the Cell (© Garland Science 2008) Plasmodesmata that join plant cells are analogous to gap junctions Figure 19-38a,b Molecular Biology of the Cell (© Garland Science 2008) Plasmodesmata are approximately 30–60 nm in diameter Figure 19-38d Molecular Biology of the Cell (© Garland Science 2008) Tissues are supported by an extracellular matrix composed of collagen fibers, proteoglycans, and adhesive proteins Collagen Provides Tensile Strength in Animal Connective Tissues Collagen fibrils are made up of collagen triplehelices aligned in a staggered fashion and crosslinked for strength The specific alignment and degree of cross-linking vary with the tissue and produce characteristic cross-striations in an electron micrograph Glycosaminoglycans • Linear polymers of repeating disaccharide units • The ionized carboxylate and sulfate groups (pink in the perspective formulas) give these polymers their characteristic high negative charge • Heparin • Chondroitin sulfate • Keratan sulfates • Hyaluronic acid Proteoglycans • Different glycosaminoglycans are linked to the core protein. • Hyaluronan and aggrecan form huge (Mr > 2 • 108) noncovalent aggregates. • They hold a lot of water (1000´ its weight) and provide lubrication. Adhesive proteins have binding sites for cellsurface receptors and ECM components Fibronectin Laminin Cells attach to the underlying extracellular matrix through two types of integrin-dependent junctions: focal adhesions and hemidesmosomes, Figure 19-3 Molecular Biology of the Cell (© Garland Science 2008) Integrin α, β heterodimers bind fibronectin, laminin, collagen, and other matrix proteins Integrins Couple the Matrix Outside a Cell to the Cytoskeleton Inside It Integrins form α, β heterodimers: When integrins are in the resting state, the α and β cytoplasmic tails are in close proximity Focal adhesions attach the actin cytoskeleton to fibers of fibronectin Stress fibers (F-actin - red) anchored at focal adhesions (vinculin -green) The FEBS Journal Volume 284, Issue 20, pages 3355-3361, 30 AUG 2017 DOI: 10.1111/febs.14195 http://onlinelibrary.wiley.com/doi/10.1111/febs.14195/full#febs14195-fig-0001 Image was kindly provided by David Graham A schematic model of focal adhesion molecular architecture Kanchanawong, et al. (2011) Nature