Elucidating the Effects of Selenium Enrichment on the Structure and Antioxidant Properties of Selenium-Containing Proteins in Yeast Cells

Selenium (Se) enrichment in yeast represents a promising strategy for producing organic Se with high bioavailability. However, a systematic understanding of how Se incorporation alters intact protein structure and function across diverse strains remains lacking. This study investigated four yeast species (Saccharomyces cerevisiae, Kluyveromyces marxianus, Kluyveromyces lactis, and Torulaspora delbrueckii) using multi-spectroscopic and radical scavenging assays. Despite moderate growth inhibition (10.4–27.7%), all strains accumulated substantial Se (1164–2858 µg/g). Structural analysis revealed that Se induced strain-dependent protein conformational perturbations. Specifically, in selenium-enriched Saccharomyces cerevisiae, where Se was predominantly incorporated as selenomethionine (SeMet, 85.80%), a significant structural relaxation occurred. This was characterized by decreased rigid β-sheet content, increased flexible random coils, and a substantial enhancement in surface hydrophobicity. Crucially, Pearson correlation analysis revealed that functional enhancements were synergistically governed by specific Se speciation and secondary structural remodeling. Enhanced DPPH• scavenging activity was positively correlated with changes in β-sheet and random coil structures. Selenomethionine content was also significantly correlated with increased scavenging of •OH and ABTS•+. Consequently, Saccharomyces cerevisiae uniquely achieved highly significant (p < 0.001) antioxidant improvements, whereas other strains showed moderate or non-significant responses despite high Se yields. Our findings demonstrate that the antioxidant efficacy of selenoproteins is not solely determined by total Se content but is fundamentally driven by the targeted bioconversion of SeMet and its associated structural relaxation.