7TE3

Crystal Structure of a Double Loop Deletion Mutant in gC1qR/C1qBP/HABP-1

Summary for 7TE3

• Entry DOI: 10.2210/pdb7te3/pdb
• Descriptor: Complement component 1 Q subcomponent-binding protein, mitochondrial (2 entities in total)
• Functional Keywords: complement, c1q-binding protein, coagulation, immune system
• Biological source: Homo sapiens (human)
• Total number of polymer chains: 1
• Total formula weight: 20030.24

Authors

Geisbrecht, B.V. (deposition date: 2022-01-04, release date: 2022-06-01, Last modification date: 2023-10-25)

Primary citation

Zhang, Y.,Vontz, A.J.,Kallenberger, E.M.,Xu, X.,Ploscariu, N.T.,Ramyar, K.X.,Garcia, B.L.,Ghebrehiwet, B.,Geisbrecht, B.V.
gC1qR/C1qBP/HABP-1: Structural Analysis of the Trimeric Core Region, Interactions With a Novel Panel of Monoclonal Antibodies, and Their Influence on Binding to FXII.
Front Immunol, 13:887742-887742, 2022

PubMed Abstract: The protein gC1qR/C1qBP/HABP-1 plays an essential role in mitochondrial biogenesis, but becomes localized at the cellular surface in numerous pathophysiological states. When this occurs on endothelial cells, surface-exposed gC1qR activates the classical pathway of complement. It also promotes assembly of a multi-protein complex comprised of coagulation factor XII (FXII), pre-kallikrein (PK), and high-molecular weight kininogen (HMWK) that activates the contact system and the kinin-generating system. Since surface-exposed gC1qR triggers intravascular inflammatory pathways, there is interest in identifying molecules that block gC1qR function. Here we further that objective by reporting the outcome of a structure/function investigation of gC1qR, its interactions with FXII, and the impact of a panel of monoclonal anti-gC1qR antibodies on FXII binding to gC1qR. Although deletion mutants have been used extensively to assess gC1qR function, none of these proteins have been characterized structurally. To that end, we determined a 2.2 Å resolution crystal structure of a gC1qR mutant lacking both of its acidic loops, but which retained nanomolar-affinity binding to FXII and FXIIa. This structure revealed that the trimeric gC1qR assembly was maintained despite loss of roughly thirty residues. Characterization of a novel panel of anti-gC1qR monoclonal antibodies identified several with biochemical properties distinct from previously described antibodies, as well as one which bound to the first acidic loop of gC1qR. Intriguingly, we found that each of these antibodies could partly inhibit binding of FXII and FXIIa to gC1qR. Based on these results and previously published studies, we offer new perspectives for developing gC1qR inhibitors.

PubMed: 35865516
DOI: 10.3389/fimmu.2022.887742

Experimental method

X-RAY DIFFRACTION (2.2 Å)