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Problem 2. (5pts) You have produced a monoclonal antibody that binds to the prot

ID: 52155 • Letter: P

Question

Problem 2. (5pts) You have produced a monoclonal antibody that binds to the protein actin. To be sure that the antibody does not cross-react with other proteins, you test your antibody in a western blot assay on whole-cell lysates that have been subjected to electrophoresis under nondenaturing conditions (shown in Figure A) and denaturing conditions (shown in Figure B). Does the antibody cross-react with other proteins? If so, does this explain the results in the two western blots? If not, how do you explain the difference observed?

Explanation / Answer

Based on the given data,

Actin is a cytoskeletal, multifunctional and globular protein (G-actin), which polymerizes and forms the long filaments of protein fibers called microfilaments or F-actin. G-actin (monomeric) protein has a molecular weight about 42 kDa, so polymerized F-actin has more than 42 kDa.

No, the Antibody does not cross-react with other proteins, it is because antibody is monoclonal, which specifically binds to actin proteins, whether they are in G or F state.

Based on the principle of electrophoresis, the low molecular weight proteins move faster than the high molecular weight proteins. In Figure-A, the Actin is in nondenaturated and F-actin polymeric state. Hence it is present in the upper region of the gel. In Figure-B, the Actin is in denaturing and G-actin polymeric state. Hence it is present in the lower region of the gel.

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