Structural Insights Into Complement Inhibition: Visualizing Distinct Binding Modes of C4b-Binding Protein Complexes With C4b and SAP
Molecular & Cellular Proteomics, vol. 24, pp. 101046
Abstract
C4b-binding protein (C4BP) is an innate immune inhibitor found in serum. Human C4BP adopts spider-like higher-order structures (HOS) formed by disulfide-linked C4BPα and C4BPβ chains that non-covalently bind vitamin K-dependent protein S (ProS). These spider-like structures can form even larger complexes as C4BP interacts with other, mostly complement-related, proteins. The complement inhibitory role of C4BP is primarily mediated through its interaction with C4b. C4BP also binds with high affinity to serum amyloid P component (SAP), a pentraxin family member associated with amyloidosis conditions. Here, we structurally and compositionally characterize C4BP interactions with these two natively occurring binders. To achieve this, we combine mass photometry, high-speed atomic force microscopy, and cross-linking mass spectrometry. By integrating the results, we reveal two distinct binding modes of C4BP when bound to C4b or SAP. Given the spider-like assembly of C4BP, C4b interacts with the N-terminal region of a single C4BPα leg, enabling multiple C4b molecules to bind to the C4BP HOS. Conversely, SAP engages with the entire spider-like HOS: the C4BPα-C4BPβ oligomerization core binds to SAP, and the C4BPα legs wrap around it.
Authors 7
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Utrecht University · Netherlands Proteomics Centre
Affiliation as printed
Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, University of Utrecht, Utrecht, the Netherlands; Netherlands Proteomics Center, Utrecht, the Netherlands
Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, University of Utrecht, Padualaan 8, Utrecht 3584 CH, the Netherlands; Netherlands Proteomics Center, Padualaan 8, Utrecht 3584 CH, the Netherlands
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University of Applied Sciences Upper Austria
Affiliation as printed
University of Applied Sciences Upper Austria, Linz, Austria
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University of Applied Sciences Upper Austria
Affiliation as printed
University of Applied Sciences Upper Austria, Linz, Austria
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Utrecht University · Netherlands Proteomics Centre
Affiliation as printed
Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, University of Utrecht, Utrecht, the Netherlands; Netherlands Proteomics Center, Utrecht, the Netherlands
Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, University of Utrecht, Padualaan 8, Utrecht 3584 CH, the Netherlands; Netherlands Proteomics Center, Padualaan 8, Utrecht 3584 CH, the Netherlands
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University of Applied Sciences Upper Austria
Affiliation as printed
University of Applied Sciences Upper Austria, Linz, Austria
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Leiden University Medical Center
Affiliation as printed
Department of Immunology, Leiden University Medical Center, Leiden, the Netherlands
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Albert J. R. Heck corresponding
Utrecht University · Netherlands Proteomics Centre
Affiliation as printed
Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, University of Utrecht, Utrecht, the Netherlands; Netherlands Proteomics Center, Utrecht, the Netherlands. Electronic address: a.j.r.heck@uu.nl
Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, University of Utrecht, Padualaan 8, Utrecht 3584 CH, the Netherlands; Netherlands Proteomics Center, Padualaan 8, Utrecht 3584 CH, the Netherlands. Electronic address: a.j.r.heck@uu.nl
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