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Nat Plants. 2017 Dec;3(12):937-945. doi: 10.1038/s41477-017-0061-1. Epub 2017 Nov 27.

Non-specific activities of the major herbicide-resistance gene BAR.

Author information

1
Whitehead Institute for Biomedical Research, Cambridge, MA, 02142, USA.
2
Department of Plant and Microbial Biology, University of Zurich, 8008, Zurich, Switzerland.
3
Institute of Medical Microbiology, University of Zurich, 8006, Zurich, Switzerland.
4
Department of Plant and Microbial Biology, University of Zurich, 8008, Zurich, Switzerland. shorten@botinst.uzh.ch.
5
Whitehead Institute for Biomedical Research, Cambridge, MA, 02142, USA. wengj@wi.mit.edu.
6
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA. wengj@wi.mit.edu.

Abstract

Bialaphos resistance (BAR) and phosphinothricin acetyltransferase (PAT) genes, which convey resistance to the broad-spectrum herbicide phosphinothricin (also known as glufosinate) via N-acetylation, have been globally used in basic plant research and genetically engineered crops 1-4 . Although early in vitro enzyme assays showed that recombinant BAR and PAT exhibit substrate preference toward phosphinothricin over the 20 proteinogenic amino acids 1 , indirect effects of BAR-containing transgenes in planta, including modified amino acid levels, have been seen but without the identification of their direct causes 5,6 . Combining metabolomics, plant genetics and biochemical approaches, we show that transgenic BAR indeed converts two plant endogenous amino acids, aminoadipate and tryptophan, to their respective N-acetylated products in several plant species. We report the crystal structures of BAR, and further delineate structural basis for its substrate selectivity and catalytic mechanism. Through structure-guided protein engineering, we generated several BAR variants that display significantly reduced non-specific activities compared with its wild-type counterpart in vivo. The transgenic expression of enzymes can result in unintended off-target metabolism arising from enzyme promiscuity. Understanding such phenomena at the mechanistic level can facilitate the design of maximally insulated systems featuring heterologously expressed enzymes.

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PMID:
29180815
PMCID:
PMC6342461
DOI:
10.1038/s41477-017-0061-1
[Indexed for MEDLINE]
Free PMC Article

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