Identification of the histidine residues of hemopexin that coordinate with heme-iron and of a receptor-binding region

• Published in: The Journal of biological chemistry 1993-03, Vol.268 (9), p.6256-6262
• Main Authors: Morgan, W T, Muster, P, Tatum, F, Kao, S M, Alam, J, Smith, A
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Analytical, structural and metabolic biochemistry; Animals; Antibodies, Monoclonal; Base Sequence; binding; Biological and medical sciences; cDNA; Chromatography, High Pressure Liquid; DNA; domains; Epitopes; Fundamental and applied biological sciences. Psychology; genes; Glycoproteins; heme; Heme - metabolism; hemopexin; Hemopexin - chemistry; Hemopexin - immunology; Hemopexin - metabolism; histidine; Histidine - analysis; Histidine - metabolism; Humans; Iron - metabolism; Molecular Sequence Data; nucleotide sequence; predictions; Proteins; Rabbits; Receptors, Cell Surface - metabolism; Receptors, Peptide; Sequence Homology, Amino Acid; Structure-Activity Relationship
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)53247-6

Rabbit hemopexin cDNA was cloned from a rabbit liver lambda gt11 cDNA expression library using a mixture of five monoclonal antibodies raised against rabbit hemopexin, and the entire rabbit hemopexin sequence was determined. The heme-binding domain I of rabbit hemopexin (Smith, A., and Morgan, W. T. (1984) J. Biol. Chem. 259, 12049-12053) contains only 4 histidine residues which are conserved in rabbit, human, rat, and mouse hemopexin. The 2 axial heme-iron coordinating histidine residues, identified by Edman microsequencing and amino acid analyses of chemically modified domain I and isolated fragments of domain I, are the conserved histidine residues at positions 56 and 127 of the mature rabbit protein. The epitope recognized by JEN-14 (a monoclonal antibody which specifically reacts with domain I and blocks the hemopexin-receptor interaction (Morgan, W. T., Muster, P., Tatum, F. M., McConnell, J., Conway, T. P., Hensley, P., and Smith, A. (1988) J. Biol. Chem. 263, 8220-8225) was shown to lie between residues 122 and 142 by Western blotting of protease-digested domain I and transposon-insertion mutants of domain I expressed in a plasmid vector system. The location of this epitope near the heme-binding histidine residue 127 is compatible with a transport mechanism in which the release of heme from hemopexin is accompanied by a concomitant transfer of heme to the hemopexin receptor or the membrane heme-binding protein (Smith, A., and Morgan, W. T. (1985) J. Biol. Chem. 260, 8325-8329).