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A heme‐ and metal‐binding hexampeptide from the sequence of rabbit plasma histidine‐rich glycoprotein
Author(s) -
Morgan William T.,
Deaciuc Victor,
Riehm John P.
Publication year - 1989
Publication title -
journal of molecular recognition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.401
H-Index - 79
eISSN - 1099-1352
pISSN - 0952-3499
DOI - 10.1002/jmr.300020304
Subject(s) - heme , histidine , chemistry , peptide , binding site , stereochemistry , peptide sequence , biochemistry , amino acid , enzyme , gene
Rabbit histidine‐rich glycorprotein (HRG) binds low‐spin heme and metal tightly at several sites that contain histidine. As part of an on‐going effort to define and locate the binding sites for these and the other ligands of HRG, the sequence: NH 2 ‐Gly‐His‐Phe‐Pro‐Phe‐His‐Trp‐… was found in a 16kDa heme‐binding peptide isolated from HRG. The spacing of the histidyl residues in this peptide, which contains the C‐terminal 79 residues of HRG, together with molecular modeling suggested that this sequence might constitute one heme binding site of HRG by accommodating heme in a bis‐histidyl linkage. Three peptides based on this sequence (I, HFPFHW; II, WHFPFH; and III, HFGFHW) were synthesized, and their ability to bind heme and metals examined. All three peptides bind heme as demonstrated by the changes produced in the absorbance of heme when mixed with the peptides. Substituting glycine for proline in the central position or moving the location of the tryptophan did not effect heme binding. The apparent K d 's of the mesoheme/peptide I, II and III complexes are 75 ± 25 μ M , indicative of heme binding approximately 100 times less avid than the mesoheme/HRG complex ( K d ca. 1 μ M ), but nearly 1000 times tighter than that of the mesoheme/histidine complex ( K d ca. 60m M ). The absorbance spectra of the mesoheme/peptide complexes, the loss of binding caused by modification of histidine residues, and the pH dependence of heme binding, all indicate that heme forms a low spin, bis‐histidyl type of complex with these peptides, like that formed with HRG itself. Copper, but not cadmium or nickel, was an effective inhibitor of heme binding by the peptides. The sequence of HRG congruent with the sequence of peptide I is proposed to be one heme‐ and metal‐binding site of rabbit HRG.