Human H-kininogen is a ferritin-binding protein.
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.
Torti
S V
SV
Department of Biochemistry, Cancer Biology, Wake Forest University School of Medicine and the Comprehensive Cancer Center of Wake Forest University, Winston-Salem, North Carolina 27157, USA.
Torti
F M
FM
D000595:Amino Acid Sequence; D015153:Blotting, Western; D005293:Ferritins / Q000378:metabolism*; D006801:Humans; D033862:Iron-Binding Proteins; D007704:Kininogens / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008024:Ligands; D008969:Molecular Sequence Data; D011485:Protein Binding; D011956:Receptors, Cell Surface / Q000302:isolation & purification / Q000378:metabolism*
D033862:Iron-Binding Proteins; D007704:Kininogens; D008024:Ligands; D011956:Receptors, Cell Surface; C027293:ferritin receptor; D005293:Ferritins