Question

For the second messenger IP3 explain what it is made from and what protein makes it. What is
its target in the cell? How and by what is it degraded? What happens to its target when it is degraded?   

Answer 1

IP3 or Inositol trisphosphate is a secondary messenger which has two functions; i) cascade the primary messenger signal intracellularly and ii) amplify the signal. This phenomena is called as signal transduction. IP3 is generated by the hydrolysis of a membrane bound phospholipid – PIP2 (phosphatidylinositol 4,5-bisphosphate). Phospholipase C – a membrane-associated enzymes that cleave phospholipids just before the phosphate is responsible for the hydrolysis of PIP2.

IP3 binds to its receptor located in endoplasmic reticulum. This binding induces the calcium ion release in the cytoplasm which in turn induces various calcium ion mediated intracellular signalling pathways.

IP3 has a half live of ~10 seconds. IP3 gets degraded in the cells by inositol polyphosphate 5-phosphatase (5-phosphatase).

IP3 and its receptor have attracted a lot of attention in the regulation of apoptotic pathways. Calcium ion signalling is responsible for the opening of mitochondrial permeability transition pore (PTP). Opening of PTP results in mitochondrial depolarization, inhibition of the respiratory chain, production of reactive oxygen species (ROS) and cell death. In case IP3 is degraded cell death (pro apoptotic) pathway will get inhibited.