ScienceAsia 49 (2023):ID 141-154 |doi:
10.2306/scienceasia1513-1874.2023.155
Chaperonin paralogues in cyanobacteria: Their non-classical
nature
Hitoshi Nakamotoa,*, Jittisak Senachakb, Apiradee Hongsthongb
ABSTRACT: Chaperonin (GroEL, Hsp60) is a molecular chaperone involved in maintaining cellular protein homeostasis.
It interacts with unfolded and misfolded proteins to assist in their folding. In this article, structures, functions,
regulation, and significance of chaperonin in cyanobacteria will be reviewed. There are multiple kinds of groEL genes
in cyanobacteria in contrast to the Escherichia coli chaperonin paradigm. The cyanobacterial groEL1 gene forms an
operon with the single groES gene, similar to the E. coli groESL operon. In contrast, the cyanobacterial groEL2 gene
is monocistronic. The regulation of expression and function of the groEL1 and groEL2 genes are mutually distinct.
Transcription of the groESL1 operon and groEL2 gene is induced not only by heat but also by light. Unlike the E. coli
groESL operon, the expression of the cyanobacterial groESL1 operon and groEL2 is not controlled by the transcription
factor sigma32. Cis-regulatory elements such as K-box and CIRCE regulate it positively and/or negatively. Combinations
of the elements in groESL1 and groEL2 are evolutionarily diversified. Functional studies suggested that GroEL1 is
equivalent to E. coli GroEL, which is essential, whereas GroEL2 is nonessential but plays an important role under stress.
The absence of GroEL2 affects proteome and phosphoproteome under stress conditions. Moreover, GroEL1 and GroEL2
are structurally different. We propose that the groEL2 gene is an outcome of neofunctionalization after groESL operon
duplication. The groEL1 gene retains the original function essential for cellular activities under both normal and stress
conditions, whereas groEL2 acquires a novel, beneficial function required under stress.
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a |
Department of Biochemistry and Molecular Biology, Graduate School of Science and Engineering, Saitama
University, Saitama 338-8570, Japan |
b |
Biosciences and System Biology Team, National Center for Genetic Engineering and Biotechnology,
National Science and Technology Development Agency at King Mongkut?s University of Technology Thonburi,
Bangkok 10150 Thailand
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* Corresponding author, E-mail: nakamoto@mail.saitama-u.ac.jp
Received 27 Oct 2022, Accepted 0 0000
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