title: Genetic and biochemical properties of streptococcal NAD-glycohydrolase inhibitor.
abstract: The gene encoding streptolysin O (slo), a cytolysin of hemolytic streptococci, is transcribed polycistronically from the promoter of the preceding NAD-glycohydrolase (NADase) gene (nga). Between nga and slo, a putative open reading frame (orf1) is located whose function has been totally unknown. Present investigation demonstrated that the orf1 encodes a protein designated as streptococcal NADase inhibitor (SNI). From its nucleotide sequence, SNI was inferred to comprise 161 amino acid residues and the deduced molecular weight was 18,800. This protein was detectable only within cells. Coexpression of SNI was essential for production of streptococcal NADase, and NADase precursor existed as an inactive complex with SNI, in recombinant Escherichia coli. Monomeric NADase and SNI rapidly formed in vitro a stable heterodimer complex in the ratio 1:1, resulting in complete suppression of the hydrolase activity. Unlike other bacterial NADase inhibitors, SNI was thermostable. This protein, coexpressed and complexed with NADase, may protect the producer cocci from exhaustion of NAD.
authors.affiliation: Department of Molecular Genetics, Faculty of Medicine, Fukui University, 23-3 Shimoaizuki, Matsuoka, Fukui, Japan. hisashi@fmsrsa.fukui-med.ac.jp
authors.forename: Hisashi
authors.initials: H
authors.lastname: Kimoto
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Fujii
authors.forename: Satoko
authors.initials: S
authors.lastname: Hirano
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Yokota
authors.forename: Akira
authors.initials: A
authors.lastname: Taketo
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000096:biosynthesis; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics; D008969:Molecular Sequence Data; D009244:NAD+ Nucleosidase / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016366:Open Reading Frames; D013291:Streptococcus / Q000201:enzymology* / Q000235:genetics*; D013301:Streptolysins / Q000096:biosynthesis
chemical_list: D001426:Bacterial Proteins; D013301:Streptolysins; C025964:streptolysin O; D009244:NAD+ Nucleosidase