What type of proteins do the alpha subunit interact with when activated?

The alpha subunit, particularly in the context of G-protein coupled receptors (GPCRs), interacts with effector proteins when activated. Upon ligand binding to the GPCR, the receptor undergoes a conformational change that activates the associated G-protein. This activation leads to the replacement of GDP with GTP on the alpha subunit, allowing it to dissociate from the beta and gamma subunits.

Once activated, the alpha subunit interacts directly with effector proteins, which are responsible for generating second messengers or initiating other signaling pathways. These effector proteins can include enzymes like adenylyl cyclase or phospholipase C, which play crucial roles in transducing the signal initiated by the receptor. This interaction ultimately leads to various physiological responses, illustrating the critical role that the alpha subunit plays in cellular signaling.

In contrast, receptor proteins are typically the targets for external signals rather than the partners for the activated alpha subunit. Structural proteins relate to the cell's mechanical integrity and organization, while transport proteins primarily deal with the movement of substances across cellular membranes, which do not directly interact with the activated alpha subunit in the context of G-proteins.