A novel divalent cation-binding site in the A domain of the beta 2 integrin CR3 (CD11b/CD18) is essential for ligand binding.
A recombinant peptide encoding the CD11b A domain bound 54Mn2+ with a high affinity. Other divalent cations, including Mg2+, Zn2+, Ni2+, Co2+, and Cd2+, but not Ca2+ or Ba2+, competed effectively for Mn2+ binding. Amino acid substitutions within two conserved and noncontiguous regions in the recombinant peptide abolished 54Mn2+ binding. When these substitutions were introduced independently in complement receptor type 3 (CR3), each abolished the metal-dependent binding of the receptor to the major C3 opsonin iC3b, without impairing subunit association or surface expression of the receptor. These findings identify an unsuspected and novel metal-binding site within the A domain of CR3 that is required for metal-dependent ligand binding and also identify a good target for designing drugs aimed at countering the inflammatory potential of this key receptor.
Michishita
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Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Charlestown 02129.
Videm
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Arnaout
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D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002412:Cations; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D004252:DNA Mutational Analysis; D008024:Ligands; D016177:Macrophage-1 Antigen / Q000737:chemistry*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins; D016415:Sequence Alignment; D012995:Solubility; D013057:Spectrum Analysis; D013329:Structure-Activity Relationship
D002412:Cations; D008024:Ligands; D016177:Macrophage-1 Antigen; D011994:Recombinant Proteins