Question

4. What type of membrane protein is this G-protein Coupled Receptor (GPCR) integral or peripheral) and describe the features that contribute to its function in the cell?

Answer 1

QUESTION 4

GPCRs are integral membrane proteins that possess seven membrane-spanning domains or transmembrane helices. GPCRs are a large family of cell surface receptors that respond to a variety of external signals. Binding of a signaling molecule to a GPCR results in G protein activation, which in turn triggers the production of any number of second messengers.

G-protein-coupled receptors (GPCRs) mediate most of our physiological responses to hormones, neurotransmitters and environmental stimulants, and so have great potential as therapeutic targets for a broad spectrum of diseases.

GPCRs can transduct signals received from messengers such as ions, organic odorants, amines, peptides, proteins, lipids, nucleotides, and even photons

GPCRs activate a number of alternative signaling cascades inside cells, enabling functional diversities.

QUESTION 5

Activation of a single G protein can affect the production of hundreds or even thousands of second messenger molecules. One especially common target of activated G proteins is adenylyl cyclase, a membrane-associated enzyme that, when activated by the GTP-bound alpha subunit, catalyzes synthesis of the second messenger cAMP from molecules of ATP. In humans, cAMP is involved in responses to sensory input, hormones, and nerve transmission, among others.

The single most frequent cancer-causing mutation across all heterotrimeric G proteins is R201C in Gαs. R201C mutation can bypass the need for GTP binding by directly activating GDP-bound Gαs through stabilization of an intramolecular hydrogen bond network.  The ability of Gαs to bind adenylyl cyclase is strongly influenced by the presence of Gβγ subunits