Abstract
Protein glycation is usually referred to as an array of non-enzymatic post-translational modifications formed by reducing sugars and carbonyl products of their degradation. The resulting advanced glycation end products (AGEs) represent a heterogeneous group of covalent adducts, known for their pro-inflammatory effects in mammals, and impacting on pathogenesis of metabolic diseases and ageing. In plants, AGEs are the markers of tissue ageing and response to environmental stressors, the most prominent of which is drought. Although water deficit enhances protein glycation in leaves, its effect on seed glycation profiles is still unknown. Moreover, the effect of drought on biological activities of seed protein in mammalian systems is still unstudied with respect to glycation. Therefore, here we address the effects of a short-term drought on the patterns of seed protein-bound AGEs and accompanying alterations in pro-inflammatory properties of seed protein in the context of seed metabolome dynamics. A short-term drought, simulated as polyethylene glycol-induced osmotic stress and applied at the stage of seed filling, resulted in the dramatic suppression of primary seed metabolism, although the secondary metabolome was minimally affected. This was accompanied with significant suppression of NF-kB activation in human SH-SY5Y neuroblastoma cells after a treatment with protein hydrolyzates, isolated from the mature seeds of drought-treated plants. This effect could not be attributed to formation of known AGEs. Most likely, the prospective anti-inflammatory effect of short-term drought is related to antioxidant effect of unknown secondary metabolite protein adducts, or down-regulation of unknown plant-specific AGEs due to suppression of energy metabolism during seed filling.
Highlights
In the most general way, protein glycation can be defined as an array of non-enzymatic post-translational modifications, formed by interaction of N-terminus and/or side chains of nucleophylic residues with reducing sugars and carbonyl products of their degradation [1]
The series of preliminary experiments, relying on assessment of physiological stress markers and the polyethylene glycol (PEG) 8000 concentration range of 2.5–10.0% (w/v) showed that already the lowest PEG concentration resulted in a 2-fold decrease of stomatal conductivity (Figure S1-2A), the other markers remained unaffected by this stressor dosage (Figure S1-2B,C)
On one hand, dehydration resulted in a significant increase in the leaf contents of abscisic acid (ABA, Figure 3F), which triggered stomata closure followed with suppression of photosystem II activity (PSII) and decrease of chlorophyll contents (Figure 3C–E), that in turn resulted in development of oxidative stress (Figure 3G)
Summary
In the most general way, protein glycation can be defined as an array of non-enzymatic post-translational modifications, formed by interaction of N-terminus and/or side chains of nucleophylic residues with reducing sugars and carbonyl products of their degradation [1]. Aldoses and ketoses, readily react with lysyl residues of proteins forming Schiff base adducts, which readily undergo further Amadori or Heyns rearrangements to yield keto- and aldoamines, respectively [2,3] (Figure 1). AGEs can be formed by so-called oxidative or autoxidative glycosylation, i.e., formation of α-dicarbonyl compounds, mostly glyoxal (GO), methylglyoxal (MGO) and 3-deoxyglucosone (3-DG), and their interaction with lysyl, arginyl and cysteinyl residues [10]. The polyol pathway [16], acetone and threonine metabolism [17] might impact on the α-dicarbonyl pool as well (Figure 1)
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