Mycobacterial chaperonins in cellular proteostasis: Evidence for chaperone function of Cpn60.1 and Cpn60.2‐mediated protein folding

• Published in: Molecular microbiology 2023-08, Vol.120 (2), p.210-223
• Main Authors: Piplani, Bakul, Kumar, C. M. Santosh, Lund, Peter A., Chaudhuri, Tapan K.
• Format: Article
• Language: English
• Subjects: ATP-Binding Cassette Transporters - metabolism; Cell division; Cell survival; chaperonin 60; Chaperonins; Chaperonins - genetics; Chaperonins - metabolism; Clients; Cystic Fibrosis Transmembrane Conductance Regulator - metabolism; Depletion; E coli; Escherichia coli; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli Proteins - metabolism; Folding; GroEL; Humans; molecular chaperones; Molecular Chaperones - metabolism; Mycobacterium tuberculosis; Mycobacterium tuberculosis - genetics; Mycobacterium tuberculosis - metabolism; Protein Folding; Proteins; Proteostasis; Thermal stability
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.15109

Mycobacterium tuberculosis encodes two chaperonin proteins, MtbCpn60.1 and MtbCpn60.2, that share substantial sequence similarity with the Escherichia coli chaperonin, GroEL. However, unlike GroEL, MtbCpn60.1 and MtbCpn60.2 purify as lower‐order oligomers. Previous studies have shown that MtbCpn60.2 can functionally replace GroEL in E. coli, while the function of MtbCpn60.1 remained an enigma. Here, we demonstrate the molecular chaperone function of MtbCpn60.1 and MtbCpn60.2, by probing their ability to assist the folding of obligate chaperonin clients, DapA, FtsE and MetK, in an E. coli strain depleted of endogenous GroEL. We show that both MtbCpn60.1 and MtbCpn60.2 support cell survival and cell division by assisting the folding of DapA and FtsE, but only MtbCpn60.2 completely rescues GroEL‐depleted E. coli cells. We also show that, unlike MtbCpn60.2, MtbCpn60.1 has limited ability to support cell growth and proliferation and assist the folding of MetK. Our findings suggest that the client pools of GroEL and MtbCpn60.2 overlap substantially, while MtbCpn60.1 folds only a small subset of GroEL clients. We conclude that the differences between MtbCpn60.1 and MtbCpn60.2 may be a consequence of their intrinsic sequence features, which affect their thermostability, efficiency, clientomes and modes of action. Mycobacterium tuberculosis encodes two enigmatic GroEL homologs, MtbCpn60.1 and MtbCpn60.2. Here, we study their functions by examining their effects on cellular phenotypes associated with obligate chaperonin clients. We show that MtbCpn60.1 supports cell survival and division to a limited extent by assisting the folding of a small subset of obligate chaperonin clients, and MtbCpn60.2 efficiently supports cell growth and proliferation by assisting the folding of a larger client pool. This is the first report demonstrating that both MtbCpn60.1 and MtbCpn60.2 are bona fide molecular chaperones.