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Unformatted text preview: r concentration of TGFß-57 released in order to achieve the maximal response. A
cell might want to regulate the number of receptors in order to direct physiological or even
f) If TGFß57 binding to its receptor had occurred with a low affinity (a Kd higher than 1X-7M),
you couldn’t have measured the Kd by performing the binding assay from above. How could you
have determined the Kd if this had been the case?
Answer: You could perform a competition assay with another ligand that binds to the
same receptor with high affinity. In this type of assay, increasing amounts of an unlabeled,
low-affinity ligand are added to a cell sample with a constant amount of the radio-labeled
high-affinity ligand. Binding of unlabeled competitor blocks binding of the radioactive
ligand to the receptor. Consequently the concentration of competitor required to inhibit
binding of half the radioactive ligand approximates the Kd value for binding if the
competitor to the receptor.
2. A colleague in your lab discovers that the binding of TGFb57 to its receptor turns on
expression of a gene that inhibits cell growth, SloGro. SloGro is frequently mutated in cancers,
and you suspect that components involved in the TGFb57 signaling pathway might also be
relevant to cancer research. You decide to set up a cell culture screen to identify proteins
involved in TGFß57 signaling. Your screen is a success, and you isolate a number of cell lines
that have mutations in the TGRb57 signaling pathway.
A) Explain how the following mutations would affect TGFb57 signaling. Assume that the basic
components of the b57 pathway are identical to the canonical TGFb signaling pa...
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- Spring '11