Solution structure of Rv2377c-founding member of the MbtH-like protein family

The Mycobacterium tuberculosis protein Rv2377c (71 residues, MW = 8.4 kDa) has been characterized using nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopy. Rv2377c was the first identified member of the MbtH-like family of proteins. MbtH-like proteins have been implicated in siderophore biosynthesis, however, their precise biochemical function remain unknown. Size exclusion chromatography and NMR spectroscopy show that Rv2377c is a monomer in solution. Circular dichroism spectroscopy indicates that Rv2377c unfolds upon heating and will reversibly fold into its native conformation upon cooling. Using NMR-based methods the solution structure of Rv2377c was determined and some of the dynamic properties of the protein studied. The protein contains a three-strand, anti-parallel β-sheet (β3:β1:β2) nestled against one C-terminal α-helix (S44-N55). Weak or absent amide cross peaks in the 1H-15N HSQC spectrum for many of the β1 and β2 residues suggest intermediate motion on the ms to μs time scale at the β1:β2 interface. Amide cross peaks in the 1H-15N HSQC spectrum are absent for all but one residue at the C-terminus (W56-D71), a region that includes a highly conserved sequence WXDXR, suggesting this region is intrinsically disordered. The latter observation differs with the crystal structure of another MbtH-like protein, PA2412 from Pseudomonas aeruginosa, where a second ordered α-helix was observed at the extreme C-terminus.