A major goal of our laboratory is to understand the mechanisms involved in cancer signaling. In many cases, the relevant signaling complexes assemble on a membrane surface, yet the role of this critical component has not been investigated. We use the Nanodics system and extensive long-term molecular dynamics simulations to define the role of the membrane in determining the structure and interactions of the oncogenic protein KRas4b with the membrane surface and with its effector proteins. The Rat sarcoma (Ras) family of small membrane-associated GTPases are essential molecules involved in a signal transduction cascade that regulate, among other cellular properties, survival and proliferation. Central to Ras-mediated signal transduction is proper transport from the endoplasmic reticulum and subsequent stable association with the lipid bilayer of the plasma membrane where, once activated, Ras recruits downstream effector proteins leading to their subsequent activation. The interaction between KRas4b and the plasma membrane is driven by hydrophobic lipid/farnesyl contacts as well as electrostatic interactions between carboxy-terminal lysine residues of KRas4b and anionic lipids. The essential interactions between Ras proteins and their associated guanine nucleotide exchange factors (GEFs), GTPase activating proteins (GAPs) and downstream signaling entities such as Raf kinases, all occur on the plasma membrane. Ras is not activated by GEFs in solution – the membrane is required. We use a new fluorescence method and the Nanodisc platform to quantitate the protein – protein and protein – lipid interactions involved in formation of the multimeric complexes at the membrane surface. By providing a means for precisely defining the lipid composition and stoichiometry that target these proteins to a localized region as well a providing sensitive assays for the association, we are in an excellent position to realize a molecular definition of the role of membrane surface electrostatics, protein-protein coupling between monomer / dimer KRas4b, GEF, GAP and effector proteins and thus defining the cooperative processes of KRas4b transport, activation and downstream signaling.