Consider the receptor tyrosine kinase (RTK) from the signaling pathway on (he pr
ID: 177144 • Letter: C
Question
Consider the receptor tyrosine kinase (RTK) from the signaling pathway on (he previous pipe. The RTK is a protein that has a single membrane-spanning domain, with a ligand binding domain that resides extracellular and a cytoplasmic ally-located kinase domain. When you look at the mRNA that encodes the RTK, you see that when translated, the RTK will have two hydrophobic domains: one at its very N-terminus and one about 1/3 rd of the way through the protein from the N-terminus. Explain why there are two hydrophobic domains, even though the RTK has a single membrane-spanning domain at the plasma membrane. In your answer, be sure to explain: a) the function of the N-terminal hydrophobic domain and b) what happens to this hydrophobic domain. The RTK will travel to the plasma membrane w ¡thin a vesicle. Draw the orientation of the RTK on a Golgi-derived vesicle (using the picture to the right), and note a) the membrane spanning hydrophobic domain. b) the ligand-binding domain, and c) the kinase domain on the drawing. Describe a mechanism that explains why the binding of Ring A to API allows API to enter the nucleus. The mechanism you propose must be consistent with what you have learned about nuclear transport. Please be as specific as possible with your answer.Explanation / Answer
RTK is acronymn for receptor tyrosine kinase. They are high affinity cell surface receptors for many polypetide growth factors , cytokines and hormones. Most RTK's are single subunit receptors but some exist as multimeric complexes. For example in insulin receptor that forms disulfide linked dimers in the presence of insulin; moreveover ligand binding to the extracellular domian induces the formation of receptor dimers. Each monomer has single hydrophobic transmembrane domain , an extracellular N-terminal region and intracellular C-terminal region.
The extracellular N-terminal region exhibits a variety of conserved elements like immunoglobulin (IgG) like, epidermal growth factors (EGF) like domain, fibronectin type III repeats or cysteine rich regions. These domian contain a ligand binding site which binds extracellular ligands for eg. particular growth factors or hormones.
The intracellular C-terminal region displays the highest level of conservation and comprises catalytic domains responsible for the kinase activity of these receptors, which catalyses receptor autphosphorylation and tyrosine phosphorylation of the RTK substrates.