Antibodies cant diffuse through the bilayer and so

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Unformatted text preview: ugh the bilayer and so the only way in which you could get fluorescence is if the epitope that the antibody is recognizing is exposed on the cell surface. Since you have a series of monoclonals whose epitope targets are known you can easily determine which parts of the protein are on the extracellular side of the membrane. (iii) If you engineer the protein to have an epitope tag e.g. HA (hemagglutinin) at the N-terminus and express the recombinant protein in cultured cells, then all you have to do is incubate the cells with an antibody against the HA tag – if it binds to the cell surface then the N-terminus (along with the HA tag) must be on the extracellular side of the membrane. You find that the protein has four cysteine residues, two on the extracellular side, two intracellularly. Which are more likely to form disulfide bonds and why? The cysteine residues that are found on the extracellular side are the only ones that could form disulfide bonds because the cytoplasm of a cell is a reducing environment and for a disulfide bond to form the sulfhydrl group of cysteine needs to oxidize. 7.06 Spring 2004 PS 1 key 11 of 11...
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