gC1qR stimulation of plasma coagulation in a FXII-dependent manner. (A) PNP was incubated for 180 seconds and increasing concentrations of gC1qR (50-200 µg/mL) with Zn²⁺ (50 µM). Coagulation was initiated by addition of CaCl₂ (8.3 mM), and clotting time was monitored. (B-F) Thrombin generation for PNP with gC1qR (50-200 µg/mL) and Zn²⁺ (50 µM). Raw data curves in the presence of gC1qR (orange) and without (gray) for lag time (minutes), endogenous thrombin potential (ETP; nM/min), peak thrombin (nM), and velocity index (nM/min) were derived. (G) Lag time (minutes) is shown for thrombin generation of PNP or FXII- or FXI-deficient plasma incubated with or without gC1qR (100 µg/mL) and Zn²⁺ (50 µM). In the absence of gC1qR, there was no thrombin generation evident in FXI- or FXII-deficient plasma. FXII-deficient plasma with gC1qR shows a significant delay in thrombin generation, with a lag time of 25 ± 6.7 minutes vs 9 ± 0.7 minutes in PNP and no thrombin generation in FXI-deficient plasma with gC1qR, indicating a dependence on the intrinsic pathway. (H) Lag time (minutes) is shown for thrombin generation of PNP, gC1qR (100 µg/mL), and gC1qR variants with G1 (cyan) and G3-loops (pink) deleted, showing a dependency on the gC1qR G3-loop.