Abstract
The ability of proteins to aggregate to form well-organized β-sheet rich amyloid fibrils is increasingly viewed as a general if regrettable property of the polypeptide chain. Aggregation leads to diseases such as amyloidosis and neurodegeneration in humans and various mammalian species but is also found in a functional variety in both animals and microbes. However, there are to our knowledge no reports of amyloid formation in plants. Plants are also the source of a large number of aggregation-inhibiting compounds. We reasoned that the two phenomena could be connected and that one of (many) preconditions for plant longevity is the ability to suppress unwanted protein aggregation. In support of this, we show that while protein extracts from the sugar maple tree Acer saccharum fibrillate readily on their own, this process is efficiently abolished by addition of small molecule extracts from the same plant. Further analysis of 44 plants showed a correlation between plant longevity and ability to inhibit protein aggregation. Extracts from the best performing plant, the sugar maple, were subjected to chromatographic fractionation, leading to the identification of a large number of compounds, many of which were shown to inhibit aggregation in vitro. One cautious interpretation is that it may have been advantageous for plants to maintain an efficient collection of aggregation-inhibiting metabolites as long as they do not impair metabolite function. From a practical perspective, our results indicate that long-lived plants may be particularly appropriate sources of new anti-aggregation compounds with therapeutic potential.
Highlights
Since the first discovery of plaque in the brains of patients suffering from Alzheimer’s disease (Masters et al, 1985), a number of proteins have been shown to form insoluble β-sheet-rich structures called amyloid or fibrils under physiological conditions (Chiti and Dobson, 2006)
thioflavin T (ThT) fluorescence increased for some protein fractions over a 5-day incubation period (Supplementary Figure S2), consistent with general formation of fibrils
There were no fibrils in F27 before extraction according to transmission electron microscopy (TEM) (Figure 1B, left), but fibril-like structures were observed after 5 days of incubation [Figure 1B(I)]
Summary
Since the first discovery of plaque in the brains of patients suffering from Alzheimer’s disease (Masters et al, 1985), a number of proteins have been shown to form insoluble β-sheet-rich structures called amyloid or fibrils under physiological conditions (Chiti and Dobson, 2006). Among these are proteins related to common diseases of lifestyle and aging such as type II diabetes (Pillay and Govender, 2013), Alzheimer’s disease, and Parkinson’s disease (Poggiolini et al, 2013) as well as rare genetic disease such as FAS4 mediated corneal dystrophy (Han et al, 2010; Stenvang et al, 2018). Examples limit themselves to a tobacco plant expressing a foreign protein (from maize) in the chloroplast (Villar-Pique et al, 2010), a coconut antimicrobial peptide which can fibrillate in aqueous buffer (Gour et al, 2016), a soya β-conglycinin subunit which fibrillates in vitro after heat treatment (Wang et al, 2011), and a protein fragment that fibrillates in vitro (Garvey et al, 2013)
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