Question

11. Understand the structure and function of: Enzyme coupled receptors (specifically RTKs): binding of growth factors, promotion of cell division and cell growth, enzymatic intracellular domain, dimerization with binding of ligand, role of kinases and tyrosine

Answer 1

Solution

RTK introduction-function

1. Receptor tyrosine kinase are the cell surface receptors bind and respond to growth factors and other locally released proteins that are present at low concentrations. RTKs play important roles in the regulation of cell growth, differentiation, and survival.
2. When signaling molecules bind to RTKs, they cause neighboring RTKs to associate with each other, forming cross-linked dimers. Cross-linking activates the tyrosine kinase activity in these RTKs through phosphorylation — specifically, each RTK in the dimer phosphorylates multiple tyrosines on the other RTK. This process is called cross-phosphorylation.

Structure of RTK-

1. Once cross-phosphorylated, the cytoplasmic tails of RTKs serve as docking platforms for various intracellular proteins involved in signal transduction.
2. These proteins have a particular domain — called SH2 — that binds to phosphorylated tyrosines in the cytoplasmic RTK receptor tails. More than one SH2-containing protein can bind at the same time to an activated RTK, allowing simultaneous activation of multiple intracellular signaling pathways.
3. Ultimately, RTK activation brings about changes in gene transcription. Signaling becomes complex as signals travel from the membrane to the nucleus, due to crosstalk between intermediates in various signaling pathways in the cell.
4.