Two-dimensional receptor patterns in the plasma membrane of cells. A critical evaluation of their identification, origin and information content

A concise review is presented on the nature, possible origin and functional significance of cell surface receptor patterns in the plasma membrane of l ymphoid cells. A special emphasize has been laid on the available methodolo gical approaches, their individual virtues and sources of errors. Fluoresce nce energy transfer is one of the oldest available means for studying non-r andomized co-distribution patterns of cell surface receptors. A detailed an d critical description is given on the generation of two-dimensional cell s urface receptor patterns based on pair-wise energy transfer measurements. A second hierarchical-level of receptor clusters have been described by elec tron and scanning force microscopies after immuno-goId-labeling of distinct receptor kinds. The origin of these receptor islands at a nanometer scale and island groups at a higher hierarchical (mu m) level, has been explained mostly by detergent insoluble glycolipid-enriched complexes known as rafts , or detergent insoluble glycolipids (DIGs). These rafts are the most-likel y organizational forces behind at least some kind of receptor clustering [K . Simons et al., Nature 387 (1997) 569]. These models, which have great sig nificance in trans-membrane signaling and intra-membrane and intracellular trafficking, are accentuating the necessity to revisit the Singer-Nicolson fluid mosaic membrane model and substitute the free protein diffusion with a restricted diffusion concept [S.J. Singer et al., Science 175 (1972) 720] . (C) 1999 Elsevier Science B.V. All rights reserved.