title: Dimeric Brucella abortus Irr protein controls its own expression and binds haem.
abstract: Brucella abortus needs to synthesize haem in order to replicate intracellularly and to produce virulence in mice. Thus, to gain insight into the pathogenesis of the bacterium, regulatory proteins of the haem biosynthetic pathway were sought. An iron response regulator (Irr) from Bradyrhizobium japonicum, which is a close relative of Brucella, was previously described as being involved in the coordination of haem biosynthesis and iron availability. The Bru. abortus genome was searched for an irr orthologue gene, and the Bru. abortus irr gene was cloned, sequenced and disrupted. A null mutant was constructed that accumulated protoporphyrin IX under conditions of iron deprivation. This phenotype was overcome by a complementing plasmid carrying the wild-type irr. Purified recombinant Bru. abortus Irr behaved as a stable dimer and bound haem. Interestingly, in vivo, Irr was only detected in cells obtained from iron-limited cultures and the protein downregulated its own transcription. Through lacZ fusion, it was demonstrated that iron did not regulate irr transcription. The data reported show that Bru. abortus Irr is a homodimeric protein that is accumulated in iron-limited cells, controls its own transcription and downregulates the biosynthesis of haem precursors.
authors.affiliation: Instituto de Investigaciones Biotecnológicas, Instituto Tecnológico de Chascomús (IIB, INTECH), Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional de General San Martín (CONICET-UNSAM), Ed 24, Av. General Paz 5445, San Martín 1650, Buenos Aires, Argentina.
authors.forename: Marcela
authors.initials: M
authors.lastname: Martínez
authors.affiliation: Instituto de Investigaciones Biotecnológicas, Instituto Tecnológico de Chascomús (IIB, INTECH), Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional de General San Martín (CONICET-UNSAM), Ed 24, Av. General Paz 5445, San Martín 1650, Buenos Aires, Argentina.
authors.forename: Rodolfo A
authors.initials: RA
authors.lastname: Ugalde
authors.affiliation: Instituto de Investigaciones Biotecnológicas, Instituto Tecnológico de Chascomús (IIB, INTECH), Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional de General San Martín (CONICET-UNSAM), Ed 24, Av. General Paz 5445, San Martín 1650, Buenos Aires, Argentina.
authors.forename: Marta
authors.initials: M
authors.lastname: Almirón
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002003:Brucella abortus / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D002417:Cattle; D003001:Cloning, Molecular; D019281:Dimerization; D015964:Gene Expression Regulation, Bacterial; D006418:Heme / Q000378:metabolism*; D006801:Humans; D007501:Iron / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D014157:Transcription Factors; C114259:iron response regulator protein, Bacteria; D006418:Heme; D007501:Iron