Solid‐phase extraction of plant thionins employing aluminum silicate based extraction columns

Thionins belong to a family of cysteine‐rich, low‐molecular‐weight (～5 KDa) biologically active proteins in the plant kingdom. They display a broad cellular toxicity against a wide range of organisms and eukaryotic cell lines. Thionins protect plants against different pathogens, including bacteria and fungi. A highly selective solid‐phase extraction method for plant thionins is reported deploying aluminum silicate (3:2 mullite) powder as a sorbent in extraction columns. Mullite was shown to considerably improve selectivity compared to a previously described zirconium silicate embedded poly(styrene‐co‐divinylbenzene) monolithic polymer. Due to the presence of aluminum(III), mullite offers electrostatic interactions for the selective isolation of cysteine‐rich proteins. In comparison to zirconium(IV) silicate, aluminum(III) silicate showed reduced interactions towards proteins which resulted into superior washings of unspecific compounds while still retaining cysteine‐rich thionins. In the presented study, European mistletoe, wheat and barley samples were subjected to solid‐phase extraction analysis for isolation of viscotoxins, purothionins and hordothionins, respectively. Matrix‐assisted laser desorption/ionization time of flight mass spectroscopy was used for determining the selectivity of the sorbent toward thionins. The selectively retained thionins were quantified by colorimetric detection using the bicinchoninic acid assay. For peptide mass‐fingerprint analysis tryptic digests of eluates were examined.