Developmental morphology and chemotactic responses are dependent on Gα subunit specificity in Dictyostelium

Dictyostelium discoideum expresses multiple Gα subunits but only a single Gβ and Gγ subunit suggesting that the specific response to an external signal depends largely on Gα subunit function or G protein-independent signaling from the receptor. To test the contribution of Gα subunit functional specificity, the chimeric Gα subunits, Gα2/4 and Gα5/4, were created and analyzed along with wild-type subunits for the ability to substitute for the Gα4 subunit in mediating responses from folate receptors. The Gα2/4 subunit, but not the Gα2 or Gα5/4 subunits, partly rescued chemotaxis and cGMP accumulation in folate-stimulated gα4− cells. Expression of the Gα5/4 or Gα5 subunits resulted in an inhibition of gα4− and wild-type cell movement and a reduced aggregate size in developing wild-type and gα5− cells suggesting these subunits mediate similar responses. Only the Gα4 subunit was capable of correcting developmental morphology in gα4− multicellular aggregates suggesting that the chimeric Gα2/4 or Gα5/4 subunits were insufficient to provide the Gα4 function necessary for proper development. These results indicate that Dictyostelium Gα subunit specificity is not limited to receptor coupling and that Gα subunit sequences outside of the carboxyl terminus are important for cell movement and developmental processes.