REGULATION OF THE BIOSYNTHESIS OF THE IRONMOLYBDENUM COFACTOR OF NITROGENASE

CURATTI L; HERNANDEZ JA ; RUBIO LM

Villa Carlos Paz

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular; 2008

Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular

Biological nitrogen fixation accounts for the major part of the global conversion of the N2 of the air into ammonium and is an essential process of the biogeochemical cycle of nitrogen that supports life on Earth. This reaction is catalyzed by the iron-molybdenum nitrogenase (MoFe nitrogenase) and alternative nitrogenases. The MoFe nitrogenase carries at its active site the unique MoFe cofactor.The synthesis of FeMo-co is a very complex process that employs the critical functions of the Nif proteins NifB, NifEN and NifH, and the participation of several other accessory factors. The NifB protein has been recently purified and shown to catalyze the synthesis of the FeMo-co precursor named NifB-co. In this work, to study regulatory features of FeMo-co biosynthesis, we uncoupled the transcription of Azotobacter vinelandii nifB gene from that of the nitrogen fixation (nif) regulon, which is derepressed when ammonium is not available and requires the transcription factor NifA. The results show the operation of a nitrogen source dependent pathway for the degradation of NifB that might involve a duplicated copy of the ClpX protein (ClpX2) in A. vinelandii. It is also apparent that the integrity of the FeMo-co biosynthesis pathway might be important for the generation of forms of NifB that are more prone to degradation by the proposed ClpX2-dependent pathway.