Journal: Science / Year: 2018 Title: Structures of C1-IgG1 provide insights into how danger pattern recognition activates complement. Authors: Deniz Ugurlar / Stuart C Howes / Bart-Jan de Kreuk / Roman I Koning / Rob N de Jong / Frank J Beurskens / Janine Schuurman / Abraham J Koster / Thomas H Sharp / Paul W H I Parren / Piet Gros / Abstract: Danger patterns on microbes or damaged host cells bind and activate C1, inducing innate immune responses and clearance through the complement cascade. How these patterns trigger complement initiation ...Danger patterns on microbes or damaged host cells bind and activate C1, inducing innate immune responses and clearance through the complement cascade. How these patterns trigger complement initiation remains elusive. Here, we present cryo-electron microscopy analyses of C1 bound to monoclonal antibodies in which we observed heterogeneous structures of single and clustered C1-immunoglobulin G1 (IgG1) hexamer complexes. Distinct C1q binding sites are observed on the two Fc-CH2 domains of each IgG molecule. These are consistent with known interactions and also reveal additional interactions, which are supported by functional IgG1-mutant analysis. Upon antibody binding, the C1q arms condense, inducing rearrangements of the C1rs proteases and tilting C1q's cone-shaped stalk. The data suggest that C1r may activate C1s within single, strained C1 complexes or between neighboring C1 complexes on surfaces.
History
Deposition
Dec 20, 2017
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Header (metadata) release
Dec 27, 2017
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Map release
Feb 28, 2018
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Update
Sep 30, 2020
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Current status
Sep 30, 2020
Processing site: PDBe / Status: Released
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Structure visualization
Movie
Surface view with section colored by density value
Cryogen name: ETHANE / Chamber humidity: 96 % / Chamber temperature: 294 K / Instrument: LEICA EM GP Details: 3 microlitres applied and incubated for 30 seconds, blot for 1 second before plunging.
Details
Extruded liposomes were incubated with IgG1 and C1. Gold fiducials were added just before applying to grids.
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Electron microscopy
Microscope
FEI TITAN KRIOS
Specialist optics
Phase plate: VOLTA PHASE PLATE / Energy filter - Name: GIF Quantum LS
Image recording
Film or detector model: GATAN K2 SUMMIT (4k x 4k) / Detector mode: COUNTING / Digitization - Dimensions - Width: 3710 pixel / Digitization - Dimensions - Height: 3838 pixel / Digitization - Sampling interval: 5.0 µm / Digitization - Frames/image: 1-6 / Average electron dose: 1.2 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Applied symmetry - Point group: C1 (asymmetric) / Algorithm: BACK PROJECTION / Resolution.type: BY AUTHOR / Resolution: 25.0 Å / Resolution method: FSC 0.143 CUT-OFF / Software - Name: Dynamo / Number subtomograms used: 1660
Extraction
Number tomograms: 34 / Number images used: 51274 / Method: Manually annotate liposome surfaces / Software - Name: Dynamo (ver. 1.1.291) Details: Equally spaced sub-volumes were extracted from the surfaces of liposomes
Final 3D classification
Software - Name: Dynamo (ver. 1.1.291)
Final angle assignment
Type: OTHER / Software - Name: Dynamo (ver. 1.1.291) Details: Volume matching after filtering reference volume to angular range present in sub-volume
FSC plot (resolution estimation)
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