title: A histidine-rich metal binding domain at the N terminus of Cu,Zn-superoxide dismutases from pathogenic bacteria: a novel strategy for metal chaperoning.
abstract: A group of Cu,Zn-superoxide dismutases from pathogenic bacteria is characterized by histidine-rich N-terminal extensions that are in a highly exposed and mobile conformation. This feature allows these proteins to be readily purified in a single step by immobilized metal affinity chromatography. The Cu,Zn-superoxide dismutases from both Haemophilus ducreyi and Haemophilus parainfluenzae display anomalous absorption spectra in the visible region due to copper binding at the N-terminal region. Reconstitution experiments of copper-free enzymes demonstrate that, under conditions of limited copper availability, this metal ion is initially bound at the N-terminal region and subsequently transferred to an active site. Evidence is provided for intermolecular pathways of copper transfer from the N-terminal domain of an enzyme subunit to an active site located on a distinct dimeric molecule. Incubation with EDTA rapidly removes copper bound at the N terminus but is much less effective on the copper ion bound at the active site. This indicates that metal binding by the N-terminal histidines is kinetically favored, but the catalytic site binds copper with higher affinity. We suggest that the histidine-rich N-terminal region constitutes a metal binding domain involved in metal uptake under conditions of metal starvation in vivo. Particular biological importance for this domain is inferred by the observation that its presence enhances the protection offered by periplasmic Cu,Zn-superoxide dismutase toward phagocytic killing.
authors.affiliation: Dipartimento di Biologia, Università di Roma "Tor Vergata," Via della Ricerca Scientifica, 00133 Rome, Italy. andrea.battistoni@uniroma2.it
authors.forename: A
authors.initials: A
authors.lastname: Battistoni
authors.forename: F
authors.initials: F
authors.lastname: Pacello
authors.forename: A P
authors.initials: AP
authors.lastname: Mazzetti
authors.forename: C
authors.initials: C
authors.lastname: Capo
authors.forename: J S
authors.initials: JS
authors.lastname: Kroll
authors.forename: P R
authors.initials: PR
authors.lastname: Langford
authors.forename: A
authors.initials: A
authors.lastname: Sansone
authors.forename: G
authors.initials: G
authors.lastname: Donnarumma
authors.forename: P
authors.initials: P
authors.lastname: Valenti
authors.forename: G
authors.initials: G
authors.lastname: Rotilio
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002845:Chromatography; D003300:Copper / Q000378:metabolism; D019281:Dimerization; D004492:Edetic Acid / Q000494:pharmacology; D010450:Endopeptidases / Q000378:metabolism; D006191:Haemophilus ducreyi / Q000201:enzymology / Q000472:pathogenicity; D006193:Haemophilus influenzae / Q000201:enzymology / Q000472:pathogenicity; D006639:Histidine / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D010587:Phagocytosis; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013482:Superoxide Dismutase / Q000737:chemistry*; D013997:Time Factors
chemical_list: D011506:Proteins; D006639:Histidine; D003300:Copper; D004492:Edetic Acid; D013482:Superoxide Dismutase; D010450:Endopeptidases