Heme binding by hemopexin: evidence for multiple modes of binding and functional implications.
Hemopexin binds 1 mol of heme per mol with high affinity (Kd < 1 pM) in a low-spin complex and acts as a transport vehicle for the heme. Circular dichroism (CD) spectroscopy was used to examine the heme environment in the ferri-, ferro-, and CO-ferro complexes of four iron tetrapyrroles [meso-, proto-, deutero-, and (2-vinyl, 4-hydroxymethyl)-deutero-heme] with three species (human, rabbit, and rat) of hemopexin. All ferri-heme-hemopexin complexes exhibit a band of positive ellipticity near the Soret maximum, except for the human ferri-protoheme hemopexin complex, which has a bisignate spectrum. The ferro-heme and CO-ferro-heme complexes display a variety of spectra, demonstrating redox- and ligand-linked shifts in conformation that alter the environment of the heme. The rabbit mesoheme-N-domain complexes have absorbance spectra almost indistinguishable from those of intact hemopexin, but present CD spectra that are distinctly different. However, adding the C-domain to mesoheme-N-domain restores most of the CD characteristics of the intact hemopexin complexes.
Shipulina
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Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, 64110, USA.
Smith
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A
Morgan
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WT
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism; D002942:Circular Dichroism; D006418:Heme / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism*; D006466:Hemopexin / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011166:Porphyrins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011817:Rabbits; D051381:Rats; D016415:Sequence Alignment; D013050:Spectrometry, Fluorescence
D002352:Carrier Proteins; D011166:Porphyrins; D006418:Heme; D006466:Hemopexin