NrdI essentiality for class Ib ribonucleotide reduction in Streptococcus pyogenes

Ignasi Roca, Eduard Torrents, Margareta Sahlin, Isidre Gibert, Britt Marie Sjöberg

Research output: Contribution to journalArticleResearchpeer-review

45 Citations (Scopus)

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. Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Original languageEnglish
Pages (from-to)4849-4858
JournalJournal of Bacteriology
Volume190
DOIs
Publication statusPublished - 1 Jul 2008

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