Characterization of a human and mouse tetrapyrrole-binding protein.
The cDNA for p22HBP has been cloned from human and mouse, and the protein expressed, purified, and characterized. Both mouse and human proteins bind heme and porphyrins with micromolar K(d)s, are highly homologous, monomeric, and soluble, and have a cytoplasmic location. The proteins bind metalloporphyrins, free porphyrins, and N-methylprotoporphyrin with similar affinities, and mutations of a selected set of putative metal ligating residues did not have any significant effect on the measured K(d)s. That the presence or absence of metal in the porphyrin has no effect on the binding constants and the observation that the EPR signal for heme does not change upon binding to the protein strongly suggest that p22HBP is a generic tetrapyrrole-binding protein rather than a dedicated heme-binding protein. A role for p22HBP in cellular porphyrin metabolism is discussed.
Jacob Blackmon
B
B
Biomedical and Health Sciences Institute, Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602-7229, USA.
Dailey
Tamara A
TA
Lianchun
Xiao
X
Dailey
Harry A
HA
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000737:chemistry; D006418:Heme / Q000378:metabolism; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D011166:Porphyrins / Q000378:metabolism; D011485:Protein Binding; D011506:Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D011758:Pyrroles / Q000378:metabolism*; D016415:Sequence Alignment; D045725:Tetrapyrroles; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; C000631029:HEBP1 protein, human; C469231:Hebp1 protein, mouse; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; D011166:Porphyrins; D011506:Proteins; D011758:Pyrroles; D045725:Tetrapyrroles; D006418:Heme