title: NrdI essentiality for class Ib ribonucleotide reduction in Streptococcus pyogenes.
abstract: The Streptococcus pyogenes genome harbors two clusters of class Ib ribonucleotide reductase genes, nrdHEF and nrdF*I*E*, and a second stand-alone nrdI gene, designated nrdI2. We show that both clusters are expressed simultaneously as two independent operons. The NrdEF enzyme is functionally active in vitro, while the NrdE*F* enzyme is not. The NrdF* protein lacks three of the six highly conserved iron-liganding side chains and cannot form a dinuclear iron site or a tyrosyl radical. In vivo, on the other hand, both operons are functional in heterologous complementation in Escherichia coli. The nrdF*I*E* operon requires the presence of the nrdI* gene, and the nrdHEF operon gained activity upon cotranscription of the heterologous nrdI gene from Streptococcus pneumoniae, while neither nrdI* nor nrdI2 from S. pyogenes rendered it active. Our results highlight the essential role of the flavodoxin NrdI protein in vivo, and we suggest that it is needed to reduce met-NrdF, thereby enabling the spontaneous reformation of the tyrosyl radical. The NrdI* flavodoxin may play a more direct role in ribonucleotide reduction by the NrdF*I*E* system. We discuss the possibility that the nrdF*I*E* operon has been horizontally transferred to S. pyogenes from Mycoplasma spp.
authors.affiliation: Departament de Genètica i de Microbiologia, Grup de Genètica Molecular Bacteriana, Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, Bellaterra, 08913 Barcelona, Spain.
authors.forename: Ignasi
authors.initials: I
authors.lastname: Roca
authors.forename: Eduard
authors.initials: E
authors.lastname: Torrents
authors.forename: Margareta
authors.initials: M
authors.lastname: Sahlin
authors.forename: Isidre
authors.initials: I
authors.lastname: Gibert
authors.forename: Britt-Marie
authors.initials: BM
authors.lastname: Sjöberg
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000235:genetics; D005418:Flavodoxin / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D023061:Gene Order; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D007501:Iron / Q000032:analysis; D009174:Mycoplasma / Q000235:genetics; D010084:Oxidation-Reduction; D012264:Ribonucleotide Reductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012265:Ribonucleotides / Q000378:metabolism*; D013057:Spectrum Analysis; D013296:Streptococcus pneumoniae / Q000235:genetics; D013297:Streptococcus pyogenes / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D005418:Flavodoxin; D012265:Ribonucleotides; D007501:Iron; C114872:NrdF protein, bacteria; D012264:Ribonucleotide Reductases