Spatial deconstruction of the plasma membrane
The plasma membrane of cells is known to be heterogeneous with regards to the spatial distribution of proteins and lipids, but the nature and origins of this heterogeneity are unclear. In this study we perform fluorescence microscopy on plasma membrane sheets and find that most proteins occur in protein-rich domains separated by intervening protein-poor regions. We show that the protein-rich domains and protein-poor regions are at least partially preserved in plasma membrane-derived vesicles that lack cytoskeletal elements, permitting their separation and isolation by density centrifugation. Compositional analysis by nuclear magnetic resonance and mass spectrometry shows that different proteins and lipids exhibit characteristic tendencies to partition into the protein-rich domains. This differential partitioning is correlated with the function of the different proteins, suggesting segregation based on cellular processes. Likewise, ordered lipids including cholesterol and sphingomyelin differentially segregate, being more abundant in the protein-rich domains. We propose that the collective assembly of certain proteins and lipids creates the heterogenous distribution of membrane components and the emergence of protein-rich domains. These domains could create distinct environments for the function and segregation of various membrane processes.