Skip to main content
ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #386376
Research Project: Sustaining Agroecosystems and Water Resources in the Northeastern U.S.

Location: Pasture Systems & Watershed Management Research

Title: Lifetimes of the AglyconeSubstrates of specifier proteins, the autonomous iron enzymes that dictate the products of the glucosinolate-myrosinase defense system in brassica plants

Author
item MOCNIAK, LEANNE - Pennsylvania State University
item Elkin, Kyle
item BOLLINGER JR, MARTIN - Pennsylvania State University

Submitted to: Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2020
Publication Date: 6/9/2020
Citation: Mocniak, L., Elkin, K.R., Bollinger, M. 2020. Lifetimes of the AglyconeSubstrates of specifier proteins, the autonomous iron enzymes that dictate the products of the glucosinolate-myrosinase defense system in brassica plants. Biochemistry. 59:2432-2441. https://doi.org/10.1021/acs.biochem.0c00358.
DOI: https://doi.org/10.1021/acs.biochem.0c00358

Interpretive Summary: Brassica plants such as kale, turnip, and broccoli are important crops for human and animal consumption, as well as cover crops for sustainable agriculture. The natural plant defense system while great for pest resistance, can prove troublesome for animal welfare causing goiter and off flavoring of milk. The study outlined here provides an understanding of an autonomous secondary enzymatic system in brassica plants that has the potential to be manipulated to increase or decrease the toxicity of the plants.

Technical Abstract: Specifier proteins (SPs) are components of the glucosinolate-myrosinase defense system found in plants of the order Brassicales (brassicas). Glucosinolates (GLSs) comprise at least 150 known S-(ß-D-glucopyranosyl)thiohydroximate-O-sulfonate compounds, each with a distinguishing side chain linked to the central carbon. Following tissue injury, the enzyme myrosinase (MYR) promiscuously hydrolyzes the common thioglycosidic linkage of GLSs to produce unstable aglycone intermediates, which can readily undergo a Lossen-like rearrangement to the corresponding organoisothiocyanates. The known SPs share a common protein architecture but redirect the breakdown of aglycones to different stable products: epithionitrile (ESP), nitrile (NSP), or thiocyanate (TFP). The different effects of these products on brassica consumers motivate efforts to understand the defense response in chemical detail. Experimental analysis of SP mechanisms is challenged by the instability of the aglycones and would be facilitated by knowledge of their lifetimes. We developed a spectrophotometric method that we used to monitor the rearrangement reactions of the MYR-generated aglycones from nine GLSs, discovering that their half-lives (t1/2) vary by a factor of more than 50, from <3 to 150 s (22 °C). The t1/2 of the sinigrin-derived allyl aglycone (34 s), which can form the epithionitrile product (1-cyano-2,3- epithiopropane) in the presence of ESP, proved to be sufficient to enable spatial and temporal separation of the MYR and ESP reactions. The results confirm recent proposals that ESP is an autonomous iron-dependent enzyme that intercepts the unstable aglycone rather than a direct effector of MYR. Knowledge of aglycone lifetimes will enable elucidation of how the various SPs reroute aglycones to different products.