Requirement for Intramolecular Domain Interaction in Activation of G Protein a Subunit by Aluminum Fluoride and GDP but Not

A n ion-counterion interaction between the lysine of the NKXD motif in the GTPase domain and an aspartate in the inserted helical domain of (Y subunits of heterotrimeric G proteins, Lys-278 andhp-158, respectively, of G p is shown to be essential for activation by AlF; and partially so for interaction with fir dimers and activation by GTP and receptor. However, this domain interaction is not required for activation by the non-hydrolyzable analog guanosine 5’-3-O-(thio)triphosphate. Proximity of the helical domain to the GTPase domain is thus involved in the fundamental inactive +active transition of the protein in a way that further distinguishes Q subunits of heterotrimeric G proteins from rus and rus-like GTPases that lack helical domains and are neither activated by A W ; nor combine with fir dimers.