Primary and secondary structure of human PF4.

(A) The crystal structure of the PF4 tetramer is shown with the lysine residues in the C terminus of PF4 (light blue) and other lysine and arginine residues (dark blue) indicated,20,21 forming the proposed heparin-binding domain. Pro37 of HIT site 1 is indicated in green. (B) The sequence of mature human and mouse PF4 (HHHH and MMMM, respectively) and human neutrophil-activating peptide-2 (NAP-2) (NNNN) are shown with identical amino acids (in single-letter codes) in the latter 2, with human PF4 shown by the colons. The conserved cysteine residues are in red and numbered at the top, dividing PF4 into 4 domains. Boxed in gray is HIT site 1.26 A major region of sequence difference between human and mouse PF4 found in the second domain.