GpaB-activated, rapA-specific guanine nucleotide exchange factor, involved in the regulation of the balance between Ras and Rap signaling at the leading edge of chemotaxing cells (PubMed:27237792, PubMed:29626371). Spatially localized activation of Rap and Ras induces F-actin polymerization at the leading edge of chemotaxing cells through the Rac, PI3K, and TORC2 pathways (PubMed:27237792). Acts also as a key regulator of actin-driven membrane protrusions during processes such as phagocytosis and cytokinesis, possibly by modulating rapA signaling pathways (PubMed:28778987). Interacts with gpaB and rapA (PubMed:27237792). Interacts directly with F-actin (PubMed:28778987). During chemotaxis, localizes at the leading edge of cells, whereas in response to cAMP stimulation, rapidly and transiently translocates to the cortex (PubMed:27237792). Localizes to F-actin-rich regions (PubMed:28778987). During macropinocytosis, strongly localizes to crowns and remains there for a short time after the cups were enclosed (PubMed:28778987). During phagocytosis of heat-killed yeast, strongly localizes to phagocytic cups with F-actin (PubMed:28778987). During cytokinesis, mainly colocalizes with F-actin at filopodia or lamellipodia of daughter cells (PubMed:28778987). The N-terminus (residues 1262 to 1601) functions to regulate both GflB-GEF activity and its localization at the leading edge of cells by binding F-actin directly. Simultaneously phosphorylated at Ser-197 and Thr-201 after cAMP stimulation. Leads to considerable chemotaxis defects, including poorer directionality, more directional changes, and slower speed (PubMed:27237792). Exhibits impaired crown formation and particularly retraction, resulting in more crowns (macropinocytic cups) per cell and longer crown lifetimes (PubMed:28778987). Leads to defects in macropinocytosis, phagocytosis and cytokinesis (PubMed:28778987). Leads to increased level of F-actin as well as to flatter and more polarized cells during vegetative growth (PubMed:28778987).