An E3 ubiquitin ligase from Brassica napus induces a typical heat-shock response in its own way in Escherichia coli

Fei Huang, Yulong Niu, Zhibin Liu, Weifeng Liu, Xufeng Li, Hong Tan, and Yi Yang

Key Laboratory of Bio-resources and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu 610065, China,

Acta Biochim Biophys Sin 2017, 49: 261–269; doi: 10.1093/abbs/gmx004

Previously, we have identified a novel E3 ubiquitin ligase, BNTR1, which plays a key role in heat stress response in Brassica napus. In this study, we accidentally found that BNTR1 can also improve thermal tolerance and reduce growth inhibition at 42°C in Escherichia coli, in a manner different from that in plant. We show that BNTR1 activates E. coli heat-shock response at low concentration in soluble form instead of in inclusion body, but BNTR1 is not functioning as a heat-shock protein (HSP) because deficient temperature-sensitive mutants of HSP genes display unconspicuous thermal tolerance in the presence of BNTR1. Our further studies show that BNTR1 triggers heat-shock response by competing with σ32 (σ32, heat-shock transcription factor) to its binding proteins DnaJ (HSP40) and DnaK (HSP70), which results in the release and accumulation of σ32, thereby promoting the heat-shock response, even under the non-heat-shock conditions. At 37°C, accumulation of the HSPs induced by BNTR1 could make cells much more tolerant than those without BNTR1 at 42°C. Thus, our results suggest that BNTR1 may potentially be a promising target in fermentation industry for reducing impact from temperature fluctuation, where E. coli works as bioreactors.

BNTR1 failed to rescue the temperature sensitivity of indicated HSP mutants

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