Chlamydia-Specific C-Terminal Region of the Stress Response Regulator HrcA Modulates Its Repressor Activity

• Published in: Journal of Bacteriology 2011-12, Vol.193 (23), p.6733-6741
• Main Authors: Chen, Allan L, Wilson, Adam C, Tan, Ming
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; binding capacity; Binding sites; Biological and medical sciences; Cell Line; Chaperonin 60 - genetics; Chaperonin 60 - metabolism; Chlamydia; Chlamydia Infections - microbiology; Chlamydia trachomatis - chemistry; Chlamydia trachomatis - genetics; Chlamydia trachomatis - metabolism; DNA-directed RNA polymerase; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial; Gene Regulation; heat shock proteins; Humans; Microbiology; Miscellaneous; Molecular Sequence Data; Protein Binding; Protein Structure, Tertiary; Proteins; Repressor Proteins - chemistry; Repressor Proteins - genetics; Repressor Proteins - metabolism; RNA polymerase; Sequence Alignment; Stress response; transcription (genetics)
• ISSN: 0021-9193; 1098-5530; 1067-8832
• DOI: 10.1128/JB.05792-11

Chlamydial heat shock proteins have important roles in Chlamydia infection and immunopathogenesis. Transcription of chlamydial heat shock genes is controlled by the stress response regulator HrcA, which binds to its cognate operator CIRCE, causing repression by steric hindrance of RNA polymerase. All Chlamydia spp. encode an HrcA protein that is larger than other bacterial orthologs because of an additional, well-conserved C-terminal region. We found that this unique C-terminal tail decreased HrcA binding to CIRCE in vitro as well as HrcA-mediated transcriptional repression in vitro and in vivo. When we isolated HrcA from chlamydiae, we only detected the full-length protein, but we found that endogenous HrcA had a higher binding affinity for CIRCE than recombinant HrcA. To examine this difference further, we tested the effect of the heat shock protein GroEL on the function of HrcA since endogenous chlamydial HrcA has been previously shown to associate with GroEL as a complex. GroEL enhanced the ability of HrcA to bind CIRCE and to repress transcription in vitro, but this stimulatory effect was greater on full-length HrcA than HrcA lacking the C-terminal tail. These findings demonstrate that the novel C-terminal tail of chlamydial HrcA is an inhibitory region and provide evidence that its negative effect on repressor function can be counteracted by GroEL. These results support a model in which GroEL functions as a corepressor that interacts with HrcA to regulate chlamydial heat shock genes.