Journal
INTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES
Volume 132, Issue -, Pages 759-765Publisher
ELSEVIER
DOI: 10.1016/j.ijbiomac.2019.04.002
Keywords
Branching enzymes; E. coli; Non-classical secretion
Funding
- National Natural Science Foundation of China [31722040, 31771935]
- China Postdoctoral Science Foundation [2018M632233]
- Fundamental Research Funds for the Central Universities [JUSRP51617B]
- National First-class Discipline Program of Food Science and Technology [JUFSTR20180204]
- Qing Lan Project
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1,4-a-Glucan branching enzyme (GBE, EC. 2.4.1.18), which plays a key role in the synthesis of starch and glycogen, has been overexpressed in E. coli as an intracellular enzyme by many researchers. In this study, it was found that the GBEs from Geobacillus thermoglucosidans and Rhodothermus obamensis were secreted into the culture medium when they were expressed separately, in E. coll. This occurred despite the absence of any signal peptide. In fact, although bioinformatics tools predicted that both of these proteins would localize to the cytoplasm, a high level of expression and non-classical secretion was found to achieve without addition of the inducer isopropyl po-thiogalactopyranoside. Further experiments revealed that secretion was a two-step process that occurred via the periplasmic space. Results excluded the involvement of the Sec pathway or the TAT pathway. Instead, the findings indicated a relationship between cell membrane integrity and the secretion of the two GBEs, and suggested that their N-termini play an essential role in their expression and secretion. (C) 2019 Elsevier B.V. All rights reserved.
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