Localization of the G protein βγ complex in living cells during chemotaxis

Gradients of chemoattractants elicit signaling events at the Leading edge of a cell even though chemoattractant receptors are uniformly distributed on the cell surface. In highly polarized Dictyostelium discoideum amoebas, membrane-associated beta gamma subunits of heterotrimeric guanine nucleotide-binding proteins (G proteins) were localized in a shallow anterior-posterior gradient. A uniformly applied chemoattractant generated binding sites for pleckstrin homology (PH) domains on the inner surface of the membrane in a pattern similar to that of the G beta gamma subunits. Loss of cell polarity resulted in uniform distribution of both the G beta gamma subunits and the sensitivity of PH domain recruitment. There observations indicate that G beta gamma subunits are not sufficiently localized to restrict signaling events to the Leading edge but that their distribution may determine the relative chemotactic sensitivity of polarized cells.