title: Regulation of the properties of superoxide dismutase from the dental pathogenic microorganism Streptococcus mutans by iron- and manganese-bound co-factor.
abstract: Streptococcus mutans, the main pathogen involved in the development of dental caries, is an aerotolerant microorganism. The bacterium lacks cytochromes and catalase, but possesses other antioxidant enzymes, such as superoxide dismutase (SmSOD). Previous researches suggested that SmSOD belongs to the 'cambialistic' group, functioning with Fe or Mn in the active site. A recombinant SmSOD (rSmSOD) with a His-tail has been produced and characterised. Studies on metal uptake and exchange proved that rSmSOD binds either Fe or Mn as a metal co-factor, even though with a consistent preference for Fe accommodation. The analysis of several enzyme samples with different values of the Mn/Fe ratio in the active site proved that the type of metal is crucial for the regulation of the activity of rSmSOD. Indeed, differently from the significant preference for Fe displayed by the enzyme in the binding reaction, its Mn-form was 71-fold more active compared to the Fe-form. The rSmSOD was endowed with a significant thermostability, its half-inactivation occurring after 10 min exposure at 71 or 73 degrees C, depending on the bound metal. Moreover, the enthalpic and entropic contribution to the heat inactivation process of rSmSOD were strongly regulated by the Mn content of the enzyme. The effect of typical inhibitors/inactivators has been investigated. rSmSOD was inhibited by sodium azide, and its sensitivity increased in the presence of higher Mn levels. Concerning two physiological inactivators, the enzyme displayed a different behaviour, being quite resistant to hydrogen peroxide and significantly sensitive to sodium peroxynitrite. Furthermore, the Mn co-factor had an amplifying role in the regulation of this different sensitivity. These results confirm the cambialistic nature of SmSOD and prove that its properties are regulated by the different metal content. The adaptative response of S. mutans during its aerobic exposure in the oral cavity could involve a different metal uptake by SmSOD.
authors.affiliation: Dipartimento di Biochimica e Biotecnologie Mediche, Università di Napoli Federico II, Via S. Pansini 5, 80131 Napoli, Italy. devendittis@dbbm.unina.it
authors.forename: Alberto
authors.initials: A
authors.lastname: De Vendittis
authors.forename: Massimo
authors.initials: M
authors.lastname: Amato
authors.forename: Andzelika
authors.initials: A
authors.lastname: Mickniewicz
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Parlato
authors.forename: Amalia
authors.initials: A
authors.lastname: De Angelis
authors.forename: Immacolata
authors.initials: I
authors.lastname: Castellano
authors.forename: Rosario
authors.initials: R
authors.lastname: Rullo
authors.forename: Francesco
authors.initials: F
authors.lastname: Riccitiello
authors.forename: Sandro
authors.initials: S
authors.lastname: Rengo
authors.forename: Mariorosario
authors.initials: M
authors.lastname: Masullo
authors.forename: Emmanuele
authors.initials: E
authors.lastname: De Vendittis
mesh_terms: D001483:Base Sequence; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D007501:Iron / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013295:Streptococcus mutans / Q000201:enzymology*; D013482:Superoxide Dismutase / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D011994:Recombinant Proteins; D008345:Manganese; D007501:Iron; D013482:Superoxide Dismutase