ClpX2 REGULATES NifB AND NifEN LEVELS DURING

MARTÍNEZ-NOËL G; CURATTI L; HERNANDEZ J; RUBIO L

Puerto Madryn

Congreso; SAIB; 2010

SAIB

Biological nitrogen fixation is mainly catalyzed by the molybdenum nitrogenase that carries at its active site the iron and molybdenum cofactor (FeMo-co). Among the genes that are required for the biosynthesis of FeMo-co nifB is remarkable because it is also essential for the biosyntheses of the cofactors all alternative nitrogenases. In this work, we show evidence suggesting the operation of a nitrogen source-dependent mechanism for the degradation of NifB and NifEN in A. vinelandii and that a duplicated copy of the ATPase component of the ClpXP protease (ClpX2) is involved in this regulatory pathway. clpX2 was induced under nitrogen fixing conditions and its inactivation slow-down NifB turnover and resulted in the accumulation of NifB and NifEN. clpX2 mutants displayed a defect in diazotrophic growth, especially when iron was limiting. Inactivation of other genes related to NifB activity (nifENX) also affected NifB degradation rates suggesting that NifB susceptibility to degradation might change during its catalytic cycle. ANPCyT.