Fig. 5: Dynamics of the IgM monomer based on smFRET and cryo-EM structure comparisons. | Nature Communications

Fig. 5: Dynamics of the IgM monomer based on smFRET and cryo-EM structure comparisons.

From: Cryomicroscopy reveals the structural basis for a flexible hinge motion in the immunoglobulin M pentamer

Fig. 5

a FRET donor (green) and acceptor (magenta) fluorescence intensity traces and the calculated FRET efficiency (blue) from a single molecule of a monomeric IgM-Fc construct labelled with the fluorophores at position 526 in the EF helix of Cμ4. The shaded area indicates when the acceptor molecule is photobleached. The histogram along the right FRET axis shows the distribution of the single-molecule FRET values for the n molecules measured. b, c Examples of single-molecule FRET traces and the respective distribution of FRET values for monomeric IgM-Fc constructs labelled at position 526 and containing either a mutation H518, which disrupts Cμ4 dimerization (b) or C-terminal coiled-coil, which forms a stable dimer (c). d Cryo-EM structure of IgM-Fc monomer with C-terminal coiled-coil showing the two-fold symmetrical arrangement at Cμ4 and Cμ3 regions (threshold 0.47). Black arrowheads indicate the density corresponding to the N-linked glycosylation at N395. e Superimposing the models of monomeric and a pentameric subunit (subunit 4 in pdb 6KXS) IgM showing similarity of the two structures, with slight variations at the orientations of Cμ3 domains. Source data are provided as a Source Data file.

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