J Biol Chem, Vol. 273, Issue 22, 13630-13635, May 29, 1998
Human H-kininogen Is a Ferritin-binding Protein
Suzy V.
Torti
and
Frank M.
Torti
From the Departments of
Biochemistry, Cancer Biology,
and
Internal Medicine, Wake Forest University School of Medicine
and the Comprehensive Cancer Center of Wake Forest University,
Winston-Salem, North Carolina 27157
H-kininogen is a multifunctional protein: it
inhibits cysteine proteases, plays a role in contact activation of the
coagulation cascade, and is the precursor of the potent proinflammatory
peptide bradykinin. In the experiments described here, we identify
H-kininogen as a ferritin-binding protein. Ferritin is a cellular and
serum protein that is elevated in acute and chronic inflammation and many cancers. Despite numerous reports of ferritin-binding protein(s) in human serum, the nature and function of these proteins remain unclear. As a first step in characterizing the interaction between ferritin and its binding protein(s), we devised a ligand blot assay and
used it to guide purification of a ferritin-binding protein from human
serum. Edman degradation of the purified protein determined the
sequence HNLGHGHK(H)ERDQGHG, a sequence with identity to residues
421-436 of human H-kininogen. These results were confirmed by
demonstrating that commercially purified H-kininogen possessed ferritin
binding activity and that ferritin binding could not be detected in
plasma from kininogen-deficient individuals. Ligand blot assays mapped
the ferritin binding domain to the light chain of H-kininogen chain,
and revealed that both H and L recombinant ferritins possess
H-kininogen binding activity. The unexpected identification of
H-kininogen as a ferritin-binding protein may link ferritin in the
complex chain of interactions by which H-kininogen mediates its
multiple effects in contact activation and inflammation.
Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.