title: Identification of NAD+ synthetase from Streptococcus sobrinus as a B-cell-stimulatory protein.
abstract: Streptococcus sobrinus, one agent of dental caries, secretes a protein that induces lymphocyte polyclonal activation of the host as a mechanism of immune evasion. We have isolated from culture supernatants of this bacterium a protein with murine B-cell-stimulatory properties and subsequently cloned the relevant gene. It contains an open reading frame of 825 bp encoding a polypeptide with 275 amino acid residues and a molecular mass of 30 kDa. The protein displays high sequence homology with NAD(+) synthetases from several organisms, including a conserved fingerprint sequence (SGGXD) characteristic of ATP pyrophosphatases. The polypeptide was expressed in Escherichia coli as a hexahistidine-tagged protein and purified in an enzymatically active form. The recombinant NAD(+) synthetase stimulates murine B cells after in vitro treatment of spleen cell cultures, as demonstrated by its ability to induce up-regulation of the expression of CD69, an early marker of lymphocyte activation. Stimulation with the recombinant NAD(+) synthetase was also observed with other B-cell markers, such as CD19(+), B220(+), and CD21(+). Cell proliferation follows the activation induced by the recombinant NAD(+) synthetase.
authors.affiliation: Instituto de Ciências Biomédicas de Abel Salazar, 4150-180 Porto, Portugal.
authors.forename: Isabel
authors.initials: I
authors.lastname: Veiga-Malta
authors.forename: Margarida
authors.initials: M
authors.lastname: Duarte
authors.forename: Márcia
authors.initials: M
authors.lastname: Dinis
authors.forename: Pedro
authors.initials: P
authors.lastname: Madureira
authors.forename: Paula
authors.initials: P
authors.lastname: Ferreira
authors.forename: Arnaldo
authors.initials: A
authors.lastname: Videira
mesh_terms: D019732:Amide Synthases / Q000302:isolation & purification* / Q000494:pharmacology; D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000096:biosynthesis; D000945:Antigens, Differentiation, T-Lymphocyte / Q000096:biosynthesis; D001402:B-Lymphocytes / Q000187:drug effects* / Q000276:immunology; D006801:Humans; D037181:Lectins, C-Type; D008213:Lymphocyte Activation / Q000187:drug effects*; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000494:pharmacology; D016986:Streptococcus sobrinus / Q000201:enzymology*; D000099192:CD69 Antigens
chemical_list: D019732:Amide Synthases; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D037181:Lectins, C-Type; D011994:Recombinant Proteins; D000099192:CD69 Antigens; C038479:NAD+ synthase