A metallomics approach discovers selenium-containing proteins in selenium-enriched soybean

Abstract

Our previous study found that high-molecular-weight selenium (Se) species make up 82% of the total Se in the bean of Se-enriched soybean plants (Chan et al. 2010, Metallomics, 2(2): p. 147-153). The Se species have been commonly seen in other plants in addition to soybean, but their identities remain unresolved. The present study employs a multi-technique metallomics approach to characterize the proteins containing Se in the beans of Se-enriched soybean plants. Two main categories of proteins, maturation proteins and protease inhibitors, were found in Se-containing high-performance liquid chromatography (HPLC) fractions. The proteins were screened by two-dimensional HPLC-inductively coupled plasma mass spectrometry, size-exclusion chromatography, and anion-exchange chromatography, and the Se-containing fractions were then identified by peptide mapping using HPLC-Chip-electrospray ion trap mass spectrometry. Based on the belief that Se goes into proteins through non-specific incorporation, a new method was designed and applied for the Se-containing peptide identification. The Se-containing peptide KSDQSSSYDDDEYSKPCCDLCMCTRS, part of the sequence of protein Bowman-Birk proteinase isoinhibitor (Glycine max), was found in one of the Se-containing fractions. The nutritional value of the Se-containing proteins in Se-enriched soybeans will be an interesting topic for the future studies.

Selenomethionine and Total Methionine Ratio is Conserved in Seed Proteins of Selenium‐Treated and Nontreated Soybean, Flax, and Potato

“…The ratio of Se-Met to the total Met pool was very well conserved between the two treatments, with a percentage Se-Met:total-Met ratio of 1.02:1.04, 1.16:1.13, and 3.67:3.39 for the Setreated:control treatments for soybean, flax, and potato, respectively (Table 4). This indicates that a large proportion of Se translocated into the seed or tuber had remained under other forms and which was separated from the protein fractions during the protein extraction process as previously reported (Brown and Shrift, 1981;Chan and Caruso, 2012). This observation indicates a low substitution of Met by Se-Met in the primary protein structure of these 3 crops when compared with wheat, where grain can contain up to 56 to 83% Se-Met (Hawkesford and Zhao, 2007).…”

“…Because of the high sensitivity of ICP-MS and MALDI-TOF MS/MS, it is unlikely that the presence of even one Se molecule would not be detected if present. But this approach may not be cost effective when compared with that described by Chan and Caruso (2012). Of the four spots selected from potato, three were successfully identified; spots P2 and P3 being identified as patatin.…”

“…This result suggests that either none of the analyzed spot samples incorporated Se or the Se level in the samples was below the detection limits of methods used in this study, despite 2 or 3 same spots were pooled for the Se analysis. Nonetheless, Chan and Caruso (2012) identified 13 unique known proteins, of which three maturation proteins (two seed maturation proteins and one maturation-like protein) and six protease inhibitors using a metallomic HPLC-Chip-ESI-ITMS analysis of Se-enriched soybean-soluble protein. It is thus reasonable to suggest that these protein spots did not incorporate Se into their backbones.…”

Comparative Studies Involving Transgenic and Non-Transgenic Soybean: What is Going On?

“…Reference [107] used different parts of the soybean plants to analyze Se elution profile using SEC-ICP-MS. The authors concluded that the bean had the most interesting profile, since it absorbed most of the Se from the shoots and presented a very intense peak for this element at higher molecular weight fraction.…”

“…Concerning multidimensional chromatographic separations and soybeans, a recent work from reference [107] used IEX as second dimension for the separation of proteins from selenium-enriched soybean. Here, the target was only Se, and the 26 fractions collected from the second dimension were pure enough to allow the identification of a considerable number of proteins in the soybean databank.…”