G-Protein-Linked Receptors

What the Hell?By:

Keven, Sam, and Cory

Basics:

• Called “g-protein linked receptors” because they BIND to the Guanine nucleotides: GDP and GTP.

• They are made of three different units (Alpha, Beta, and Gamma) that attach to:– The inner surface of the plasma

membrane – “Transmembrane” receptors (G protein-

coupled receptors, GPCRs for short).

How Do They Work? A wannabe, smart biologist asks..

In the inactive

state, Gα (g-protein) has GDP in its

binding site When a hormone or

other “ligand” binds to GPCR, an allosteric

change takes place in the

receptor

After the bind, the G-

protein separates

into Ga and GβGγ

subunits

GTP activates

Gα causing it to

dissociate from GβGγ-

which remains as

two subunits.

Activated Gα activates an adenylyl

cyclase, an enzyme in the inner plasma membrane,

which catalyzes the conversion of ATP into cAMP.

Activated Gα is now a GTPase so it quickly

converts its GTP back to GDP.

This conversion, tied with the return of the Gβ and Gγ subunits,

restores the G protein to its inactive

state

In other words.. or pictures..

CholeraWell…What the Hell is it?

Cholera is an infection in the small intestine caused by the bacterium Vibrio Cholerae.

What happens on the cellular level?• The Cholera toxin, an enzyme, transfers ADP from NAD+

(an enzyme that transfers hydrogen) and adds it to a chain in the Gsa protein.

• This prevents the GTP from hydrolysis, so that the Gsa chain is left permanently in the stimulatory state.

• In essence, the cholera toxin enters the body through intestinal cells, it exerts a volume of fluid which expels and becomes far more than the intestinal system can handle.

• THUS, causing a large amount of watery diarrhea. WHEW OUTTA BREATH

Epinepherine Well…What the Hell is it (part II)?

• Epinephrine Animation