Lecture 3: GPCRs And Signal Transduction Flashcards
How many membrane spanning alpha helices does the common core of a GPCR have?
Seven.
Is the C-terminus of a GPCR located extracellularly or intracellularly?
Intracellularly.
How many classes of GPCRs are there?
Six.
What is unique about class A protease-activated GPCRs?
The N-terminus of these protease-activated receptors is cleaved off in order to activate it. This cannot be reversed and a whole new receptor has to be made afterwards.
Which class of GPCRs have an extracellular domain that resembles a Venus fly trap? And give two examples.
Class C. For example metabotropic glutamate receptors and GABAb receptors.
What is a G-protein made up of? And why is it called a heterotrimer?
Heterotrimer -> hetero = different + trimer = three -> three different subunits. It is made up of alpha, beta and gamma subunits.
When the receptor is not bound to a ligand, where is the G-protein?
It can be either nearby or be pre-coupled to the receptor. The alpha subunit is bound to GDP nonetheless.
What happens when GTP binds to the alpha subunit?
The alpha subunit dissociates from the receptor and the beta-gamma complex. Leaving three separate sections: the receptor, the alpha subunit bound to GTP, and the beta-gamma complex.
The identity of which subunit classifies G-proteins?
The alpha subunit.
What is adenylate cyclase?
A membrane-bound enzyme that converts ATP to cAMP.
What does beta-arrestin do?
Binds to phosphorylated receptors and induces their endocytosis and therefore downregulation. Receptors are then either recycled back or degraded. This is a desensitisation response to the agonist.
What does arrestin-mediated ubiquitination of a receptor lead to?
Degradation by lysosomes.
