You are interested in the function of a protein, Mtm1, that has a PH domain, an
ID: 64212 • Letter: Y
Question
You are interested in the function of a protein, Mtm1, that has a PH domain, an SH3 domain, and a PTB domain. Mtm1 functions downstream of the insulin receptor and binds to this receptor in an insulin-dependent fashion via its PTB domain. You create mutant forms of Mtm1 that delete the various protein domains. You find that these mutations do not seem to affect the protein level or folding of Mim1. You examine the localization of Mtm1 and your results are summarized in Table 2. In Table 2, the D symbol indicates that the following protein domain is deleted. For example, mtm1DPH indicates an Mtm1 protein that lacks the PH domain; mtm1DPHDSH3 indicates an mtm1 protein that lacks both the PH domain and the SH3 domain. Given what you know about these three protein domains and the data above, explain the role of the PH, PTB, and SH3 domains in localizing the Mtm1 protein.Explanation / Answer
PH domains play a role in recruiting proteins to different membranes, thus targeting them to appropriate cellular compartments or enabling them to interact with other components of the signal transduction pathways.
SH3 domains play a role in the signalling pathways regulating cytoskeleton, Ras protein etc. They are thought to increase the substrate specificity of proteins by binding far away from the active site of the proteins.
PTB are protein domains which bind to phosphotyrosine. Insulin receptor substrate-1 contains both PH and PTB domains.
When the insulin is bound to the receptor, the Mtm1 protein is localised to the membrane.
The deletion mutation of SH3 domain has no effect on the localization of Mtm 1 protein to the membrane.
The deletion mutation of PH domain has a mild effect, due to which only some of the Mtm 1 protein is localised to the membrane the rest in the cytoplasm.
The deletion mutation of PTB domain has more effect than PH domain. Most of the protein is localised to the cytoplasm.
The double deletion of PH and PTB has drastic effect on the Mtm 1 protein localisation, as no protein is bound to the membrane even in the presence of insulin. This clearly shows PH, PTB and Mtm 1 protein interaction is important for mediating the insulin signalling into the cell.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.