Ribosomal protein L2 associates with E. coli HtpG and activates its ATPase activity

Although eukaryotic Hsp90 has been studied extensively, the function of its bacterial homologue HtpG remains elusive. Here we report that 50S ribosomal protein L2 was found as an associated protein with His-tagged HtpG from Escherichia coli cultured in minimum medium at 45 °C. L2 specifically activated ATPase activity of HtpG, but other denatured proteins did not. The analysis using domain derivatives of HtpG and L2 showed that C-terminal domain of L2 and the middle to C-terminal domain of HtpG are important for interaction. At physiological salt concentration, L2 was denatured state and was recognized by HtpG as well as other chaperones, DnaK/DnaJ/GrpE and GroEL/GroES. The ATPase of HtpG at increasing concentration of L2 indicated that an L2 molecule bound to a dimer HtpG with apparent KD of 0.3 μM at 100 mM KCl and 3.3 μM at 200 mM KCl.

Research highlights
► L2 was found as an associated protein with HtpG from E. coli cells.
► L2 specifically activated the ATPase activity of HtpG.
► The C-terminal domain of L2 and the middle to C-terminal domain of HtpG interact.
► L2 was denatured state at physiological salt concentration.
► The dissociation constant between HtpG and L2 was determined.