title: Mechanisms for size-dependent protein segregation at immune synapses assessed with molecular rulers.
abstract: Immunological synapses are specialized intercellular contacts formed by several types of immune cells in contact with target cells or antigen-presenting cells. A late-stage immune synapse is commonly a bulls-eye pattern of immune cell receptor-ligand pairs surrounded by integrin complexes. Based on crystal structures, the intermembrane distance would be ∼15 nm for many immune cell receptor-ligand pairs, but ∼40 nm for integrin-ligand pairs. Close proximity of these two classes of intermembrane bonds would require significant membrane bending and such proteins can segregate according to their size, which may be key for receptor triggering. However, tools available to evaluate the intermembrane organization of the synapse are limited. Here, we present what we believe to be a novel approach to test the importance of size in the intercellular organization of proteins, using live-cell microscopy of a size-series of fluorescently-labeled molecules and quantum dots to act as molecular rulers. Small particles readily colocalized at the synapse with MHC class I bound to its cognate natural killer cell receptor, whereas particles larger than 15 nm were increasingly segregated from this interaction. Combined with modeling of the partitioning of the particles by scaled-particle adsorption theory, these molecular rulers show how membrane-bending elasticity can drive size-dependent exclusion of proteins within immune synapses.
authors.affiliation: Sir Alexander Fleming Building, Division of Cell and Molecular Biology, Imperial College London, London, UK.
authors.forename: Juha-Matti
authors.initials: JM
authors.lastname: Alakoskela
authors.forename: Apurba L
authors.initials: AL
authors.lastname: Koner
authors.forename: Dominika
authors.initials: D
authors.lastname: Rudnicka
authors.forename: Karsten
authors.initials: K
authors.lastname: Köhler
authors.forename: Mark
authors.initials: M
authors.lastname: Howarth
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Davis
mesh_terms: D045744:Cell Line, Tumor; D004548:Elasticity; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D015236:HLA-C Antigens / Q000378:metabolism; D006801:Humans; D054992:Immunological Synapses / Q000378:metabolism*; D018799:Intercellular Adhesion Molecule-1 / Q000737:chemistry / Q000378:metabolism; D010316:Particle Size; D011506:Proteins / Q000378:metabolism*; D045663:Quantum Dots; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D005456:Fluorescent Dyes; D015236:HLA-C Antigens; C528994:HLA-C*06 antigen; D011506:Proteins; D011993:Recombinant Fusion Proteins; D018799:Intercellular Adhesion Molecule-1; D049452:Green Fluorescent Proteins