Gproteiinide

Gproteiinide, known in English as G-proteins, are a family of guanine nucleotide-binding proteins that play a critical role in transmitting signals from various stimuli outside a cell to its interior. They are involved in numerous cellular processes, including regulation of enzyme activity, ion channels, and other signaling pathways.

G-proteins are typically composed of three subunits: alpha (α), beta (β), and gamma (γ). When a signaling molecule, such as a hormone or neurotransmitter, binds to a receptor on the cell surface, it often activates a G-protein associated with that receptor. In its inactive form, the G-protein has GDP bound to its alpha subunit. Activation involves exchange of GDP for GTP, causing a conformational change that allows the G-protein to interact with and modulate target effector proteins.

There are two main types of G-proteins: heterotrimeric G-proteins, which are membrane-bound and composed of the three subunits, and small GTPases, which are monomeric. Heterotrimeric G-proteins are primarily involved in receptor-mediated signaling pathways, such as those linked to G-protein-coupled receptors (GPCRs). Small GTPases, like Ras, regulate cell growth, differentiation, and motility.

The activity of G-proteins is tightly regulated by other proteins such as GTPase-activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs). Dysregulation of G-proteins has been implicated in various diseases, including cancers, making them important targets for pharmacological intervention.

Overall, G-proteins are essential components of cellular signaling mechanisms, facilitating communication within cells and coordinating responses to external signals.