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Combining SPR with atomic-force microscopy enables singlemolecule insights into activation and suppression of the complement cascade

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Makou_2019_JBC_SPR_CC.pdf (2.861Mb)
Date
27/12/2019
Author
Makou, Elisavet
Bailey, Richard G.
Johnston, Heather
Parkin, John D.
Hulme, Alison N.
Hähner, Georg
Barlow, Paul N.
Keywords
Surface plasmon resonance (SPR)
Atomic force microscopy (AFM)
Complement system
Protein-protein interaction
Protein conformation
Inflammation
Single-molecule biophysics
C3b
Factor H
Immune response
Molecular stretching
Self-assembling monolayer
Single-molecule analysis
QH301 Biology
Biochemistry
Molecular Biology
Cell Biology
NDAS
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Abstract
Activation and suppression of the complement system compete on every serum-exposed surface, host or foreign. Potentially harmful outcomes of this competition depend on surface molecules through mechanisms that remain incompletely understood. Combining surface plasmon resonance (SPR) with atomic force microscopy (AFM), here we studied two complement system proteins at the single-molecule level: C3b, the proteolytically activated form of C3, and factor H (FH), the surface-sensing C3b-binding complement regulator. We used SPR to monitor complement initiation occurring through a positive-feedback loop wherein surface-deposited C3b participates in convertases that cleave C3, thereby depositing more C3b. Over multiple cycles of flowing factor B, factor D, and C3 over the SPR chip, we amplified C3b from ∼20 to ∼220 molecules·μm−2. AFM revealed C3b clusters of up to 20 molecules and solitary C3b molecules deposited up to 200 nm away from the clusters. A force of 0.17 ± 0.02 nanonewtons was needed to pull a single FH molecule, anchored to the AFM probe, from its complex with surface-attached C3b. The extent to which FH molecules stretched before detachment varied widely among complexes. Performing force-distance measurements with FH(D1119G), a variant lacking one of the C3b-binding sites and causing atypical hemolytic uremic syndrome, we found that it detached more uniformly and easily. In further SPR experiments, KD values between FH and C3b on a custom-made chip surface were 5-fold tighter than on commercial chips and similar to those on erythrocytes. These results suggest that the chemistry at the surface on which FH acts drives conformational adjustments that are functionally critical.
Citation
Makou , E , Bailey , R G , Johnston , H , Parkin , J D , Hulme , A N , Hähner , G & Barlow , P N 2019 , ' Combining SPR with atomic-force microscopy enables singlemolecule insights into activation and suppression of the complement cascade ' , Journal of Biological Chemistry , vol. 294 , no. 52 , pp. 20148-20163 . https://doi.org/10.1074/jbc.RA119.010913
Publication
Journal of Biological Chemistry
Status
Peer reviewed
DOI
https://doi.org/10.1074/jbc.RA119.010913
ISSN
0021-9258
Type
Journal article
Rights
Copyright © 2019 Makou et al. Final version open access under the terms of the Creative Commons CC-BY license.
Description
This work was supported by Leverhulme Trust Grant RPG-2015-109.
Collections
  • University of St Andrews Research
URI
http://hdl.handle.net/10023/19318

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