Aggregation and mobility of membrane proteins interplay with local lipid order in the plasma membrane of T cells

Abstract

To disentangle the elusive lipid–protein interactions in T‐cell activation, we investigate how externally imposed variations in mobility of key membrane proteins (T‐cell receptor [TCR], kinase Lck, and phosphatase CD45) affect the local lipid order and protein colocalisation. Using spectral imaging with polarity‐sensitive membrane probes in model membranes and live Jurkat T cells, we find that partial immobilisation of proteins (including TCR) by aggregation or ligand binding changes their preference towards a more ordered lipid environment, which can recruit Lck. Our data suggest that the cellular membrane is poised to modulate the frequency of protein encounters upon alterations of their mobility, for example in ligand binding, which offers new mechanistic insight into the involvement of lipid‐mediated interactions in membrane‐hosted signalling events.

Influence of the extracellular domain size on the dynamic behavior of membrane proteins

“…There are currently multiple mechanisms proposed for T cell signaling (and most are applicable to other immune cell types). Size-dependent, lipid-dependent, or diffusion-dependent exclusion of inhibitory molecules (such as CD45) from the immune synapse are three of the main and seemingly distant mechanisms explaining T-cell signaling (3–8). However, our results suggest that all three phenomena can be intertwined.…”

“…Multiple mechanisms are proposed to explain the initial protein reorganization that leads to the activation (phosphorylation) of the receptors. Partitioning of signaling proteins into membrane domains (2), their ECD size (3–5), their allosteric interactions with lipids (6), and their mobility altered by the ligands (7, 8) are some examples of these mechanisms. Although there is compelling evidence for each of these mechanisms for immune signaling, the dominating mechanism is still unclear.…”

Imaging Membrane Order and Dynamic Interactions in Living Cells with a DNA Zipper Probe

“…Thee xistence of lipid order plays an important role in the formation of TCR signaling complexes. [4][5][6][7][46][47][48][49][50] Membrane order can act as aplatform to allow TCRs to interact with kinases and trigger signaling cascades that promote T-cell proliferation and differentiation. [50] To test if the DNAZipper can be used to investigate lipid order formation due to the onset of TCR signaling, we first studied the hybridization efficiencyofDNAprobes in amodel T-cell membrane,t he CD4 + Jurkat E6-1 cell line,w hich has been widely used for studying TCR signaling.…”

Significance of Receptor Mobility in Multivalent Binding on Lipid Membranes

“…Thek inetics of membrane components is ac entral parameter in receptor/ligand binding.T he diffusive lipid bilayer provides ad ynamic platform for embedded proteins (receptors), whose mobility was shown to play ap ivotal role in various biological processes,i ncluding Tcell activation [1] and the formation of stable focal adhesions. [2] In particular, membrane mobility is often relevant for multivalent interactions,w here al igand with multiple binding sites engages an umber of receptors present on the surface, [3,4] while monovalent interactions are too weak to ensure stable binding (Figure 1a).…”

“…[30] Here we will not dissect these intricate mobility changes,b ut focus on the universal importance of kinetics in multivalent binding.Inthis Minireview we argue as imple,g eneralised idea behind dynamic multivalency:f inding ab alance between welldefined, energetically favourable interactions,while allowing for ac ertain range of adjustability to reduce its dependency on the non-significant environmental variations, [31] as well as provide the means for the cell to control vital signalling processes. [1,2,32]…”