HK amino acid sequences and interaction with FXI. (A) The HK C-terminal domain 6 amino acid sequence alignment derived from the National Center for Biotechnology Information HOMOLOGENE server for different species is indicated. Conserved residues across >50% of the sequences are shaded black (highly conserved) or gray (weak conservation) with the program BOXSHADE. Peptides P27 and P31 from the random screen that match sequences within HK domain 6 are shown aligned. Dashed lines represent the sequence of synthetic peptides HKP and HKC. ★ indicates residue Ile563, which is the location of a venous thrombosis risk factor–associated human missense mutation Ile563Thr, located directly N-terminal to the HK ISDFP sequence. Plots of SPR sensorgrams measured in response units (RU) illustrate peptide P39 (B) and HKP (C) binding to immobilized FXI, and FXI binding to immobilized HK (D). (E) Binding of the HKC peptide to immobilized FXI.