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Journal of Bacteriology, January 2004, p. 419-426, Vol. 186, No. 2
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.2.419-426.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Identification of NAD+ Synthetase from Streptococcus sobrinus as a B-Cell-Stimulatory Protein{dagger}

Isabel Veiga-Malta,1,2 Margarida Duarte,1,2 Márcia Dinis,1,2 Pedro Madureira,1 Paula Ferreira,1,2 and Arnaldo Videira1,2*

Instituto de Ciências Biomédicas de Abel Salazar,1 Instituto de Biologia Molecular e Celular, 4150-180 Porto, Portugal2

Received 15 July 2003/ Accepted 14 October 2003

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.

* Corresponding author. Mailing address: Instituto de Biologia Molecular e Celular, Rua do Campo Alegre 823, 4150-180 Porto, Portugal. Phone: 351-226074900. Fax: 351-226099157. E-mail: asvideir{at}icbas.up.pt.

{dagger} This article is dedicated to the memory of Mário Arala Chaves.

Journal of Bacteriology, January 2004, p. 419-426, Vol. 186, No. 2
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.2.419-426.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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