A scientist is studying a signal transduction pathway that is controlled by a re

Question

A scientist is studying a signal transduction pathway that is controlled by a receptor tyrosine kinase and has identified a MAP kinase that functions as part of the signaling cascade. She engineers an altered form of the MAP kinase in which residues that are phosphorylated when the signaling pathway is turned on are replaced with amino acids that cannot be phosphorylated. What affect would this have on the signaling pathway? The scientist has also identified a GTP-ase that is involved in an interaction with the receptor after it dimerizes. What would be the effect on signaling of adding GTPgS to tissue culture cells expressing the mutated version of the MAP kinase? (Note - GTPgS can bind to GTPases but cannot be converted to GDP). Explain your answers.

Explanation / Answer

The MAPK pathway, when it is activaded it triggers a phosporylation cascade, which means that one component needs to be activaded (phosporylated) in order to activate the next component by a phosporylation, this process happens in specific amino acid residues, in this case residues of serine or threonine.

If the scientist modify this residues, it will cause a stop of the phosporylation cascade, because the components can not be activaded therefore the process that this pathway regulates such as cell proliferation, differentiation, survival and apoptosis are suspended.

With respect to the second question, the MAPK pathway begins with the activation of a small GTP-ase called RAS, which become activated when it is bind to GTP; now GTPgS it is an agonist which induce the activation of the GTP-ase, so, adding this component to the cells with the mutant MAPK it will result in the activation of RAS (saturation of the system, because it can not be desactivaded since GTPgS it is not converted in to GDP) but the rest of the pathway stays the same, meaning that the phosporylation cascade remains suspended.

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