Purification and biochemical characterization of DnaK and its transcriptional activator RpoH from Neisseria gonorrhoeae

• Published in: Molecular biology reports 2014-12, Vol.41 (12), p.7945-7953
• Main Authors: Narayanan, Shalini, Beckham, Simone A., Davies, John K., Roujeinikova, Anna
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animal Anatomy; Animal Biochemistry; Bacterial Proteins - chemistry; Bacterial Proteins - isolation & purification; Bacterial Proteins - metabolism; Biochemistry; Biomedical and Life Sciences; Cloning, Molecular; Escherichia coli; Gene expression; Gonorrhea; Heat-Shock Proteins - isolation & purification; Heat-Shock Proteins - metabolism; Histology; HSP70 Heat-Shock Proteins - genetics; HSP70 Heat-Shock Proteins - isolation & purification; HSP70 Heat-Shock Proteins - metabolism; Kinetics; Life Sciences; Molecular Sequence Data; Morphology; Neisseria gonorrhoeae; Neisseria gonorrhoeae - enzymology; Neisseria gonorrhoeae - genetics; Neisseria gonorrhoeae - metabolism; Promoter Regions, Genetic; Sigma Factor - isolation & purification; Sigma Factor - metabolism; Stress response
• ISSN: 0301-4851; 1573-4978
• DOI: 10.1007/s11033-014-3689-1

DnaK plays a central role in stress response in the important human pathogen Neisseria gonorrhoeae. The genes encoding the DnaK chaperone machine (DnaK/DnaJ/GrpE) in N. gonorrhoeae are transcribed from RpoH (σ 32 )-dependent promoters. In this study, we cloned, purified and biochemically characterised N. gonorrhoeae DnaK ( Ng DnaK) and RpoH. The Ng DnaK and RpoH sequences are 73 and 50 % identical to the sequences of their respective E. coli counterparts. Similar to Ec DnaK, nucleotide-free Ng DnaK exists as a mix of monomers, dimers and higher oligomeric species in solution, and dissociates into monomers on addition of ATP. Like E. coli σ 32 , RpoH of N. gonorrhoeae is monomeric in solution. Kinetic analysis of the basal ATPase activity of purified Ng DnaK revealed a V max of 193 pmol phosphate released per minute per microgram DnaK (which is significantly higher than reported basal ATPase activity of Ec DnaK), and the turnover number against ATP was 0.4 min −1 under our assay conditions. Nucleotide-free Ng DnaK bound a short model substrate, NR-peptide, with micromolar affinity close to that reported for Ec DnaK. Our analysis showed that interaction between N. gonorrhoeae RpoH and DnaK appears to be ATP-dependent and non-specific, in stark contrast to the E. coli DnaK system where σ 32 and DnaK interact as monomers even in the absence of ATP. Sequence comparison showed that the DnaK-binding site of σ 32 is not conserved in RpoH. Our findings suggest that the mechanism of DnaK/RpoH recognition in N. gonorrhoeae is different from that in E. coli .