Characterization of human NFU and its interaction with the molecular chaperone system
How iron-sulfur clusters are syntheisized in vivo remains an interesting topic to explore. In this dissertation, studies were focused on human NFU, an important protein that participates in iron-sulfur cluster biosynthesis. Studies were first carried out on NFU’s functional characterization. Due to the presence of the conserved CXXC motif in NFU, this protein was proposed and demonstrated to cleave the persulfide bond on NifS. In the presence of L-cysteine, a catalytic amount of NifS, ferrous iron and NFU, apo proteins lacking iron-sulfur clusters can be successfully reconstituted. The function of human NFU led to the hypothesis that this protein can interact with NifS. The binding of NFU to NifS was quantified by ITC (isothermal titration calorimetry). The temperature-dependence of binding was also examined to determine the underlying thermodynamics. A positive change in enthalpy with increased temperature suggested dominance of polar charged residues in the binding. The interaction of human NFU and the chaperone system was also studied in vitro. Both NFU and its C-terminal domain can stimulate the ATPase activity of the chaperone HscA. The ADP form of HscA binds to both NFU and the C-terminal domain more tightly than the ATP form, providing additional evidence for NFU interacting with the chaperone system. The binding of NFU to the HscA/HscB complex is tighter than binding to HscA alone, which is consistent with previous ATPase results. Besides functional characterization, structural characterization was also carried out. The near UV CD data for NFU were almost negligible, suggesting a possible molten globule property of human NFU. Results from ANS binding and tryptic digestion experiments were consistent with molten globule type proteins. Tryptic digestion suggested the rigid tertiary structure of the N-terminal domain. It was confirmed to possess a tertiary structure by the ANS experiment and the tryptic digestion experiment.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:nfu nifs iron sulfur cluster molten globule molecular chaperone
Date of Publication:01/01/2007