Structures of factor XI and prekallikrein bound to domain 6 of high-molecular weight kininogen reveal alternate domain 6 conformations and exosites

Background: High-molecular weight kininogen (HK) circulates in plasma as a complex with zymogen prekallikrein (PK). HK is both a substrate and a cofactor for activated plasma kallikrein, and the principal exosite interactions occur between PK N-terminal apple domains and the C-terminal D6 domain of HK.Objectives: To determine the structure of the complex formed between PK apple domains and an HKD6 fragment and compare this with the coagulation factor XI (FXI)-HK complex. Methods: We produced recombinant FXI and PK heavy chains (HCs) spanning all 4 apple domains. We cocrystallized PKHC (and subsequently FXIHC) with a 31-amino acid synthetic peptide spanning HK residues Ser565-Lys595 and determined the crystal structure. We also analyzed the full-length FXI-HK complex in solution using hydrogen deuterium exchange mass spectrometry.Results: The 2.3 & ANGS; PKHC-HK peptide crystal structure revealed that the HKD6 sequence WIPDIQ (Trp569-Gln574) binds to the apple 1 domain and HK FNPISDFPDT (Phe582-Thr591) binds to the apple 2 domain with a flexible intervening sequence resulting in a bent double conformation. A second 3.2 & ANGS; FXIHC-HK peptide crystal structure revealed a similar interaction with the apple 2 domain but an alternate, straightened conformation of the HK peptide where residues LSFN (Leu579-Asn583) interacts with a unique pocket formed between the apple 2 and 3 domains. HDX-MS of full length FXI-HK complex in solution confirmed interactions with both apple 2 and apple 3.Conclusions: The alternate conformations and exosite binding of the HKD6 peptide likely reflects the diverging relationship of HK to the functions of PK and FXI.

Automated summary

The structure of the complex formed between HK and PK apple domains was determined, revealing different conformations and interactions compared to the FXI-HK complex.