Multiple chaperonins in bacteria—novel functions and non-canonical behaviors

Abstract

Chaperonins are a class of molecular chaperones that assemble into a large double ring architecture with each ring constituting seven to nine subunits and enclosing a cavity for substrate encapsulation. The well-studied Escherichia coli chaperonin GroEL binds non-native substrates and encapsulates them in the cavity thereby sequestering the substrates from unfavorable conditions and allowing the substrates to fold. Using this mechanism, GroEL assists folding of about 10-15 % of cellular proteins. Surprisingly, about 30 % of the bacteria express multiple chaperonin genes. The presence of multiple chaperonins raises questions on whether they increase general chaperoning ability in the cell or have developed specific novel cellular roles. Although the latter view is widely supported, evidence for the former is beginning to appear. Some of these chaperonins can functionally replace GroEL in E. coli and are generally indispensable, while others are ineffective and likewise are dispensable. Additionally, moonlighting functions for several chaperonins have been demonstrated, indicating a functional diversity among the chaperonins. Furthermore, proteomic studies have identified diverse substrate pools for multiple chaperonins. We review the current perception on multiple chaperonins and their physiological and functional specificities.

Chloroplast Chaperonin: An Intricate Protein Folding Machine for Photosynthesis

“…Although some mitochondria and bacteria also possess more than one chaperonin subunit, it is still a fascinating question why the chloroplast uniquely contains divergent Cpn60 α/β chaperonin subunits as well as Cpn10/20 co-chaperonin types (Kumar et al, 2015 ). Transcriptome and proteome studies in Arabidopisis indicated expression levels of chaperonin and co-chaperonin genes differ according to developmental stage (Weiss et al, 2009 ), which increases the complex potential of the chaperonin system for regulation on both transcriptional and post-translational levels.…”

Biofilm-Constructing Variants of Paraburkholderia phytofirmans PsJN Outcompete the Wild-Type Form in Free-Living and Static Conditions but Not In Planta

“…GroEL was recently described as a pathogen-associated molecular pattern (PAMP) that triggers PAMP-triggered immunity (PTI) in Arabidopsis (69). Finally, GroEL plays a significant role in the adherence and subsequent biofilm formation in many bacteria (70). PGPRs were previously described to use phase variation to avoid stimulation of the host's immune system (23,36).…”

The Role of GroE Chaperonins in Developing Biocatalysts for Biofuel and Chemical Production

“…Transcriptome analysis in the innate ethanol producer S. cerevisiae reviewed that HSP33 and HSP104 were up-regulated when their functional conformations. A recent study systematically analyzed the GroE dependent proteins in E. coli, and found that 57 proteins could not be active in their native host E. coli without a well-functioning GroE chaperone system [31,32]. Moreover, it has been demonstrated that the E. coli xylose isomerase and arabinose isomerase, both previously reported as being non-functional in yeast [33,34], can work well in S. cerevisiae via co-expression of E. coli GroE [35].…”

“…Unlike other proteins with highly specific targets, chaperones have a broad range of substrates. For instance, the bacterial HSP60 chaperone, GroEL and its co-chaperone, GroES, which together assemble the GroE complex, work on numerous proteins [29,31,32], and GroE increases E. coli tolerance towards heat shock extreme or sudden changes in temperature. Previous studies reported that the overexpression of prokaryotic GroE can alleviate the inhibitory effects of various end-products on engineered strains [27].…”