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Factor XII and kininogen asymmetric assembly with gC1qR/C1QBP/P32 is governed by allostery

DOI: 10.1182/blood.2020004818 DOI Help

Authors: Bubacarr G. Kaira (University of Nottingham) , Alexandre Slater (University of Birmingham) , Keith R. Mccrae , Ingrid Dreveny (University of Nottingham) , Um-May Sumya (University of Aberdeen) , Nicola J. Mutch (University of Aberdeen) , Mark Searle (University of Nottingham) , Jonas Emsley (University of Nottingham)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Blood

State: Published (Approved)
Published: June 2020
Diamond Proposal Number(s): 19880

Abstract: The contact system is composed of Factor XII (FXII), prekallikrein (PK) and co-factor kininogen (HK). The globular C1q receptor (gC1qR) has been shown to interact with FXII and HK. We reveal the FXII fibronectin type II domain (FnII) binds gC1qR in a Zn2+ dependent fashion and determined the complex crystal structure. FXIIFnII binds the gC1qR trimer in an asymmetric fashion with residues Arg36 and Arg65 forming contacts with two distinct negatively charged pockets. gC1qR residues Asp185 and His187 coordinate a Zn2+ adjacent to the FXII binding site and a comparison with the ligand free gC1qR crystal structure reveals the anionic G1-loop becomes ordered upon FXIIFnII binding. Additional conformational changes in the region of the Zn2+ binding site reveal an allosteric basis for Zn2+ modulation of FXII binding. Mutagenesis coupled with SPR demonstrate the gC1qR Zn2+ site contributes to FXII binding and plasma based assays reveal gC1qR stimulates coagulation in a FXII-dependent manner. Analysis of the binding of HK domain 5 (HKD5) to gC1qR shows only one high affinity binding site per trimer. Mutagenesis studies identify a critical G3-loop located at the center of the gC1qR trimer suggesting steric occlusion as the mechanism for HKD5 asymmetric binding. Gel filtration experiments reveal that gC1qR clusters FXII and HK into a higher order 500kDa ternary complex. These results support the conclusion that extracellular gC1qR can act as a chaperone to cluster contact factors which may be a prelude for initiating the cascades which drive bradykinin generation and the intrinsic pathway of coagulation.

Journal Keywords: factor xii; fibronectins; bradykinin; complement 1q receptors; contact factors; gel chromatography; ligands; molecular chaperones; prekallikrein; crystal structure

Diamond Keywords: Thrombosis

Subject Areas: Biology and Bio-materials, Chemistry


Instruments: I03-Macromolecular Crystallography

Added On: 02/07/2020 08:51

Discipline Tags:

Life Sciences & Biotech Health & Wellbeing Non-Communicable Diseases Structural biology

Technical Tags:

Diffraction Macromolecular Crystallography (MX)