Interplay of sHsp sequestrases and protein disaggregases in extreme bacterial stress resistance

• Applicant: Privatdozent Dr. Axel Mogk
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms ; Biochemistry
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 566933605

Bacteria as single-celled organisms are particularly exposed to environmental stress conditions challenging protein homeostasis. This demands for a sophisticated protein quality control (PQC) network protecting cells from protein unfolding and aggregation. Small heat shock proteins (sHsps) are central components of PQC systems. The bacterial sHsp member IbpA binds misfolded proteins to sequester them in IbpA/substrate complexes. Dissociation and reactivation of IbpA-bound substrates requires the activity of a disaggregation activity executed by the canonical Hsp70/ClpB disaggregase. Bacteria can acquire additional sHsps and protein disaggregases raising the question whether the expansions of their sHsp and disaggregase repertories are functionally linked. The presence of novel sHsps might also allow for optimized adaptation to environmental growth conditions and provide enhanced stress resistance. Here, we will use the major pathogen Pseudomonas aeruginosa as model system to dissect whether and how the expansion of sHsp and disaggregase repertoires is linked to the acquisition of extreme stress resistance protecting bacteria against temperature-based sterilization protocols used in food industry and clinics. P. aeruginosa harbors Hsp20 and ClpG as novel sHsp and disaggregase members. Both genes are coorganized on the mobile tLST island, which provides extreme stress resistance. Our initial data indicate specific Hsp20 features, separating it from the canonical IbpA sHsp. These features include a temperature-based activity control and a specific cooperation with the ClpG disaggregase. By combining our complementary expertises in chaperone biochemistry and P. aeruginosa genetics and physiology we plan to: (1) Determine the substrate pools of IbpA and Hsp20 under diverse stress conditions and dissect the mechanistic basis of the differing sHsp substrate specificities. (2) Determine the consequences of extreme temperatures on sHsp activities and stabilities and their individual contributions to bacterial survival at extreme temperatures. (3) Determine the mode of the selective interplay of sHsps and protein disaggregases and the relevance of sHsp/disaggregase cooperations in bacterial resistance against severe stress.

• DFG Programme: Research Grants
• International Connection: South Korea
• Partner Organisation: National Research Foundation of Korea, NRF
• Cooperation Partner: Professor Changhan Lee, Ph.D.