Probing Colocalization of N-Ras and K-Ras4B Lipoproteins in Model Biomembranes.

Signaling of N-Ras and K-Ras4B proteins depends strongly on their correct localization in the cell membrane. In vivo studies suggest that intermolecular interactions foster the self-association of both N-Ras and K-Ras4B and the formation of nanoclusters in the cell membrane. As sites for effector binding, nanocluster formation is thought to be essential for effective signal transmission of both N-Ras and K-Ras4B. To shed more light on the spatial arrangement and mechanism underlying the proposed cross-talk between spatially segregated Ras proteins, the simultaneous localization of N-Ras and K-Ras4B and their effect on the lateral organization of a heterogeneous model biomembrane has been studied by using AFM and FRET methodology. It is shown that, owing to the different natures of their membrane anchor systems, N-Ras and K-Ras4B not only avoid assembly in bulk solution and do not colocalize, but rather form individual nanoclusters that diffuse independently in the fluid membrane plane.