The NifX Protein is Involved in the Final Stages of FeMo-cofactor Transport to the MoFe Protein

Abstract

The nitrogenase enzyme catalyzes the reduction of dinitrogen to ammonia and is composed of the Fe and MoFe proteins. The iron molybdenum cofactor (FeMo-co) of the MoFe protein is the site of active substrate reduction. The NifX protein has also been suggested to have a role in the FeMo-co synthesis, although its exact role is still open to investigation. We attempted to understand the role of NifX by determining the specific interactions it may have with other Nif proteins involved in FeMo-co synthesis, such as NifD, NifK, NifN, NifDK and NifH. Using the BacterioMatch Two-Hybrid System, a translationally fused construct of NifX with the N-terminal α-RNAP of the pTRG target vector was made and its interaction was tested with the NifDK fusion protein, translationally fused to the λCI of the pBT vector. The strength of the interaction, as determined by measuring the β-galactosidase activity, demonstrated that direct protein-protein interaction exists between NifDK and NifX proteins; the extent of interaction between NifK and NifX proteins was much higher than between NifD and NifX, when individually tested; also, reduced interaction was found between NifH and NifX.