Encapsulation of Mannose-6-phosphate Isomerase in Yeast Spores and Its Application in l-Ribose Production

Polysaccharide biosynthetic pathway profiling and homologous expression of the phosphomannomutase gene in Sanghuangporus sanghuang based on multi-omics analysis

Sanghuangprous sanghuang is a valuable medicinal macrofungus with abundant active metabolites. Improvement of macrofungal strains to increase the production of metabolites, especially polysaccharides, has become a research priority. In this study, we sequenced the whole genome and transcriptome of S. sanghuang SS-01 strain, identified the genes of key enzymes involved in the polysaccharide synthetic pathway, and constructed a homologous recombinant strain to increase S. sanghuang polysaccharide (SSP) yield for the first time. The assembled genome is 37.83 Mb with 22 contigs, encoding 7266 predicted genes. Forty putative genes related to sugar metabolism were identified, and the proposed SSP synthetic pathway was mapped. Transcriptional profiling was performed under different culture conditions to investigate the importance of key gene expression on SSP content. The phosphomannomutase (SsPMM) gene, which showed a strong correlation with SSP production, was identified from six differentially expressed genes. Based on the polyethylene glycol-mediated protoplast transformation system, a homologous recombinant strain (RsPMM) was obtained. The upregulated expression level of SsPMM (1.39-fold) was associated with significantly higher SSP content (1.46-fold) in RsPMM compared to the wild-type strain. Our findings provide an effective approach to increase polysaccharide production and facilitate the understanding of metabolite synthesis mechanisms in S. sanghuang.

Establishment of a Novel Platform for Developing Oral Vaccines Based on the Surface Display System of Yeast Spores

Oral vaccines are currently the focus of vaccine development because they are convenient to administer, easy to distribute, and capable of activating mucosal immunity. However, the complexity of the gastrointestinal environment and the lack of delivery vehicles severely limit the stability and effectiveness of oral vaccines. This study established a novel platform for developing oral vaccines based on the surface display system of yeast spores. As a specific example, oral vaccines for COVID-19, designed by displaying the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein on the surface of three Saccharomyces cerevisiae spore types, including AN120, osw2Δ, and dit1Δ, were constructed and evaluated. The displayed RBD showed perfect gastrointestinal stability in vitro and was validated in animal studies to produce effective humoral immunity and significant mucosal immune responses after the vaccination. Notably, the displayed RBD elicited a cellular immune response skewed towards a T-helper type 1 (Th1) cell direction in a mouse model. Our findings proved that the oral vaccines of S. cerevisiae spores could rapidly induce a comprehensive and protective immune response to SARS-CoV-2. This study aims to provide a promising and potentially useful system that can be used to develop other oral vaccines.

Green biotechnological synthesis of rare sugars/alcohols: D-allulose, allitol, D-tagatose, L-xylulose, L-ribose

Rare sugars are paid more attention because of which have the characteristics of low calorie, low absorption and excellent physiological functions. Biotechnological synthesis of rare sugars has the advantages of being green, clean, simple and economic compared to chemical synthesis. Abundant enzymes for rare sugars biosynthesis are introduced and multienzyme cascade catalytic system (MECCS) used in biosynthesis of rare sugars is highlighted in this paper. Different biosynthesis pathways of five important rare sugars (D-allulose, allitol, D-tagatose, L-xylulose, l-ribose), mainly containing isomerization/epimerization reaction (existing thermodynamic equilibrium limitation), reduction-oxidation reaction (needing expensive cofactors) and phosphorylation-dephosphorylation reaction pathways (inherent constraint of thermodynamic equilibrium and requirement high-cost cofactors) etc., are reviewed. Furthermore, techniques of cofactor regeneration and enzyme/cell immobilization are provided. Finally, unique insights and expectations for future development in biosynthesis of rare sugars are given. This review provides a comprehensive analysis of the latest biotechnological advancements in the biosynthesis of rare sugars/alcohols, highlighting innovative multienzyme cascade catalytic systems and cofactor regeneration strategies.

Establishment of a Novel Cell Surface Display Platform Based on Natural "Chitosan Beads" of Yeast Spores

Cell surface display technology, which expresses and anchors proteins on the surface of microbial cells, has broad application prospects in many fields, such as protein library screening, biocatalysis, and biosensor development. However, traditional cell surface display systems have disadvantages: the molecular weight of phage display proteins cannot be too large; bacterial display lacks the post-translational modification process for eukaryotic proteins; yeast display is prone to excessive protein glycosylation and misfolding of multisubunit proteins; and the compatibility of Bacillus subtilis spore display needs to be further improved. Therefore, it is extremely valuable to develop an efficient surface display platform with strong universality and stress resistance properties. Although yeast surface display systems have been extensively investigated, the establishment of a surface display platform using yeast spores has rarely been reported. In this study, a novel cell surface display platform based on natural "chitosan beads" of yeast spores was developed. The target protein in fusion with the chitosan affinity protein (CAP) exhibited strong binding capability with "chitosan beads" of yeast spores in vitro and in vivo. Moreover, this protein display system showed highly preferable enzymatic properties and stability. As an example, the displayed LXYL-P1-2-CAP demonstrated high thermostability and reusability (60% of the initial activity after seven cycles of reuse), high storage stability (75% of original activity after 8 weeks), and excellent tolerance to a concentration up to 75% (v/v) organic reagents. To prove the practicability of this surface display system, the semisynthesis of paclitaxel intermediate was demonstrated and its highest conversion rate was 92% using 0.25 mM substrate. This study provides a novel and useful platform for the surface display of proteins, especially for multimeric macromolecular proteins of eukaryotic origin.