TITLE:
Heterologous Expression of Thermolabile Proteins Enhances Thermotolerance in Escherichia coli
AUTHORS:
Yuya Ueda, Seiji Yamauchi, Shinsuke Fukata, Hidetoshi Okuyama, Eugene Hayato Morita, Rahul Mahadev Shelake, Hidenori Hayashi
KEYWORDS:
Heat Shock Proteins, σ32, Psychrophilic Proteins, Thermotolerance
JOURNAL NAME:
Advances in Microbiology,
Vol.6 No.9,
August
2,
2016
ABSTRACT: Heat shock proteins
(HSPs) play important roles in the mechanism of cellular protection against
various environmental stresses. It is well known that accumulation of misfolded
proteins in a cell triggers the HSPs expression in prokaryotes as well as
eukaryotes. In this study, we heterologously expressed two proteins in E.
coli, namely, citrate synthase (CpCSY) and malate dehydrogenase (CpMDH)
from a psychrophilic bacterium Colwellia psychrerythraea 34H (optimal
growth temperature 8°C). Our analyses using circular dichromism along
with temperature-dependant enzyme activities measured in purified or direct
cell extracts confirmed that the CpCSY and CpMDH are thermolabile
and present in misfolded form even at physiological growth temperature. We
observed that the cellular levels of HSPs, both GroEL and DnaK cheperonins were
increased. Similarly, higher levels were observed for sigma factor s32 which is specific to
heat-shock protein expression. These results suggest that the
misfolded-thermolabile proteins expressed in E. coli induced the heat
shock response. Furthermore, heat treatment (53°C) to wild type E.
coli noticeably delayed their growth recovery but cells expressing CpCSY
and CpMDH recovered their growth much faster than that of wild type E.
coli. This reveals that the HSPs expressed in response to
misfolded-thermolabile proteins protected E. coli against heat-induced
damage. This novel approach may be a useful tool for investigating stress-tolerance
mechanisms of E. coli.