D103 - Lecture 10 - Protein Sorting.docx

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Biological Sciences
Grant Mac Gregor

A. Clicker a. Embryonic structure - mixed cells - require cadherins to interact with Ca2+ i. Ca2+ reveals the binding domains on the cadherins ii. Which buffer to use? 1. pH, CaCl2 b. Test if a N-terminus of a protein is NECESSARY for directing protein into nucleus i. Tells necessary vs sufficient 1. Could be necessary but not sufficient ii. Tag GFP iii. Fuse to protein iv. Remove N-terminus A. Cadherins a. Also engages in bi-directional signaling. (http://www.biology.northwestern.edu/igp/faculty/green/) b. Mediates the connection between F-actin of neighboring cells i. Creates an adhesion belt 1. Used for motility and folding of the epithelial layer b. Interact with actin -> adhesion belt c. Interacts with intermediate filaments -> desmosomes B. Intermediate Filament Binding Proteins a. Links cadherin to intermediate filaments i. Connects IF between cells b. Desmosome i. Connects IF between cells ii. Provides framework strength b. Pemphigus i. Autoimmune ii. Antibodies that attack desmosomal cadherins iii. Cells cannot attach to each other iv. Another disease? Collagen B. Adhesion belt a. Actin links between cells b. Allows for epithelial cells to bend B. Tight Junctions a. Selectively permeable barrier between cells b. Epithelial cells i. Apical and basolateral surfaces have different protein composition b. Composed mainly of claudins i. Forms selective channels ii. Different combination iii. Necessary and sufficient for a tight junction b. Function i. Molecular sieve 1. Prevents molecules from the apical membrane to move between cells ii. Separates apical and basolateral membranes 1. Separates the membrane proteins from mixing B. Protein Transport within the cell a. Function of organelle i. Protein composition ii. Lipid composition iii. Position B. Protein Sorting a. Sorting Signal (ticket) i. Necessary and sufficient ii. Interacts with a receptor b. Translocation-Competent State i. Usually unfolded protein b. Receptor c. Translocation machinery d. Driving force e. Release from machinery and folding B. Protein sorting in Cytosol a. Cytosolic ribosome is transiently attached to the rER i. Only one pool of ribosomes b. Sorting signal i. Required for transport out of the cytosol B. Sorting Signal a. Necessary b. Sufficient i. Moves neutral protein to new compartment ii. GFP is normally expressed
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