Tn-Ras, Synaptotagmin1 C2ab, Annexinb12 And Amphiphysin Nbar Can Discriminate Spherical From Cylindrical Membrane Curvature

Membrane shape or geometrical curvature emerged recently as a potent regulator of membrane recruitment during protein trafficking and sorting. Cellular membranes display distinct curvature geometries e.g. spherical (trafficking- and synaptic vesicles) or cylindrical (tubes in the ER and Golgi), however quantitative studies of protein recruitment by membrane curvature typically focus on a single geometry. Thus the biological implications of different curvature geometries remain largely unexplored.We recently used our single liposome assay to show that the N-Ras lipid anchor (tN-Ras) is recruited by spherical membrane curvature. Here we report the development of a novel membrane tube assay, allowing us to quantitatively compare the recruitment of tN-Ras by spherical and cylindrical membrane curvature. Furthermore we expand the study to include representatives of the four most common families of membrane-binding domains (MBDs); the lipid anchor of N-Ras (tN-Ras), the C2AB-domain of Synaptotagmin1 (Syt), AnnexinB12 (Anx) and Amphiphysin NBAR (Amph). Our data revealed an increased recruitment of all four MBDs by spherical as compared to cylindrical curvature. Molecular field theory calculations attributed this trend to the greater perturbation of lipid packing parameters by spherically curved membranes. Importantly, the four MBDs displayed markedly distinct abilities to discriminate the two curvature geometries e.g. tN-Ras had a moderate 2-fold discrimination while Amph a remarkable absolute preference for spherical membranes. This demonstrated that discrimination of curvature geometry can be modulated and likely adapted to specific biological functions. Our results reveal membrane curvature geometry as a novel regulator of protein recruitment during trafficking and sorting for a plethora of membrane-binding proteins, and thus suggest a novel functional role to the diversity of conserved organelle morphologies.