Abstract Number: OC 74.4
Meeting: ISTH 2022 Congress
Theme: Coagulation and Natural Anticoagulants » Contact Pathway
Background: During contact activation, the plasma protein FXII binds to polyanionic surfaces through its heavy chain, and undergoes autocatalytic conversion to the protease FXIIa. Previously we showed that the first epidermal growth factor (EGF1) domain of FXII is required for autoactivation on polyphosphate, kaolin and ellagic acid. EGF1 contains twelve basic amino acids including a patch of highly conserved lysines residues that could mediate polyanion-binding.
Aims: Identify FXII amino acids involved in surface-binding and autoactivation.
Methods: FXII with alanine replacements for Lys73, Lys74 and Lys76, alone (FXII-Ala73, FXII-Ala74, FXII-Ala76) or in combination (FXII-Ala73-76) were expressed. FXII- with EGF1 replaced with EGF1 from the FXII-homolog Pro-HGFA (FXII-EGF1) served as control. FXII autoactivation was assessed with negatively charged substances (polyphosphate, dextran sulfate, heparin, ellagic acid, kaolin, and silica). Binding was assessed by pull-down experiments with heparin and kaolin.
Results: FXII autoactivated on all substances tested while FXII-EGF1 did not. While FXII-Ala73, FXII-Ala74, FXII-Ala76 autoactivated similarly to FXII on all surfaces, FXII-Ala73-76 failed to autoactivate with polyphosphate, dextran sulfate or heparin. FXII-Ala73-76 autoactivated with ellagic acid, kaolin, and silica. FXII-Ala73, FXII-Ala74, FXII-Ala76 bound heparin more weakly than FXII, while FXII-Ala73-76 did not bind heparin. All proteins appeared to bind kaolin normally.
Conclusion(s): A cluster of basic amino acids at the N-terminus of the FXII EGF1 domain mediates binding and supports FXII autoactivation with the soluble polyanions polyphosphate, heparin and dextran sulfate. However, these residues are not required for autoactivation on insoluble surfaces such as kaolin, silica or ellagic acid. As the chimera FXII-EGF1 fails to autoactivate on soluble and insoluble surfaces, it appears that different parts of EGF1 support autoactivation, depending on the type of surface.
To cite this abstract in AMA style:
Shamanaev A, Litvak M, Dickeson S, Gailani D. Identification of a site on Factor XII required for interactions with polyphosphate and other soluble polyanions [abstract]. https://abstracts.isth.org/abstract/identification-of-a-site-on-factor-xii-required-for-interactions-with-polyphosphate-and-other-soluble-polyanions/. Accessed September 24, 2023.« Back to ISTH 2022 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/identification-of-a-site-on-factor-xii-required-for-interactions-with-polyphosphate-and-other-soluble-polyanions/