Identification of sulfhydryl-containing proteins and further evaluation of the selenium-tagged redox homeostasis-regulating proteins.

Chemoproteomic profiling of sulfhydryl-containing proteins has consistently been an attractive research hotspot. However, there remains a dearth of probes that are specifically designed for sulfhydryl-containing proteins, possessing sufficient reactivity, specificity, distinctive isotopic signature, as well as efficient labeling and evaluation capabilities for proteins implicated in the regulation of redox homeostasis. Here, the specific selenium-containing probes (Se-probes) in this work displayed high specificity and reactivity toward cysteine thiols on small molecules, peptides and purified proteins and showed very good competitive effect of proteins labeling in gel-ABPP. We identified more than 6000 candidate proteins. In TOP-ABPP, we investigated the peptide labeled by Se-probes, which revealed a distinct isotopic envelope pattern of selenium in both the primary and secondary mass spectra. This unique pattern can provide compelling evidence for identifying redox regulatory proteins and other target peptides. Furthermore, our examiation of post-translational modification (PTMs) of the cysteine site residues showed that oxidation PTMs was predominantly observed. We anticipate that Se-probes will enable broader and deeper proteome-wide profiling of sulfhydryl-containing proteins, provide an ideal tool for focusing on proteins that regulate redox homeostasis and advance the development of innovative selenium-based pharmaceuticals.

Selenium-oxidizing Agrobacterium sp. T3F4 steadily colonizes in soil promoting selenium uptake by pak choi (Brassica campestris).

Selenium (Se) deficiency in soil is linked to its low content in edible crops, resulting in adverse impacts on the health of 15% of the global population. The crop mainly absorbs oxidized selenate and selenite from soil, then converts them into organic Se. However, the role of Se-oxidizing bacteria in soil Se oxidation, Se bioavailability and Se absorption into plants remains unclear. The strain Agrobacterium sp. T3F4, isolated from seleniferous soil, was able to oxidize elemental Se into selenite under pure culture conditions. The green fluorescent protein (gfp)-gene-marked strain (T3F4-GFP) and elemental Se or selenite (5 mg·kg-1) were added to pak choi (Brassica campestris ssp. chinensis) pot cultures. Observation of the fluorescence and viable counting indicated that GFP-expressing bacterial cells steadily colonized the soil in the pots and the leaves of the pak choi, reaching up to 6.6 × 106 and 2.0 × 105 CFU g-1 at 21 days post cultivation, respectively. Moreover, the total Se content (mostly organic Se) was significantly increased in the pak choi under T3F4 inoculated pot culture, with elemental Se(0) being oxidized into Se(IV), and soil Se(IV) being dissolved before being absorbed by the crop. After strain T3F4 was inoculated, no significant differences in microbial diversity were observed in the soils and roots, whereas the abundance of Rhizobium spp. was significantly increased. To our knowledge, this is the first time that Se-oxidizing Agrobacterium sp. T3F4 has been found to steadily colonize soil and plant tissues, and that its addition to soil increases the absorption of Se in plants. This study provides a potential strategy for Se biofortification.