Rapid parallel flow cytometry assays of active GTPases using effector beads

We describe a rapid assay for measuring the cellular activity of small guanine triphosphatases (GTPases) in response to a specific stimulus. Effector-functionalized beads are used to quantify in parallel multiple GTP-bound GTPases in the same cell lysate by flow cytometry. In a biologically relevant example, five different Ras family GTPases are shown for the first time to be involved in a concerted signaling cascade downstream of receptor ligation by Sin Nombre hantavirus.