Gfehérjéket

Gfehérjéket, often referred to as G proteins, are a family of intracellular signal transducers. They play a crucial role in cellular communication, mediating the effects of hormones, neurotransmitters, and other extracellular signals. G proteins are a type of GTPase, meaning they bind and hydrolyze guanosine triphosphate (GTP). They are typically heterotrimeric, composed of three distinct subunits: alpha (α), beta (β), and gamma (γ).

The G protein cycle begins when an extracellular signal binds to a transmembrane receptor, known as a G protein-coupled receptor (GPCR). This binding event causes a conformational change in the GPCR, which in turn activates the associated G protein. In its inactive state, the alpha subunit is bound to guanosine diphosphate (GDP). Upon activation, the GPCR facilitates the exchange of GDP for GTP on the alpha subunit.

Once GTP is bound, the G protein becomes activated, and the alpha subunit dissociates from the beta-gamma dimer. Both the activated alpha subunit (bound to GTP) and the beta-gamma dimer can then interact with and modulate the activity of downstream effector proteins. These effectors can include enzymes, such as adenylyl cyclase or phospholipase C, or ion channels. The specific effector targeted depends on the type of G protein involved.

The cellular response initiated by the activated effector then propagates the signal. Eventually, the alpha subunit hydrolyzes its bound GTP back to GDP, which leads to its reassociation with the beta-gamma dimer, returning the G protein to its inactive state and terminating the signal. This intricate cycle allows for precise control over cellular processes in response to a wide array of external stimuli.