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BackgroundHuman lysozyme (hLYZ), an emerging antibacterial agent, has extensive application in the food and pharmaceutical industries. However, the source of hLYZ is particularly limited.ResultsTo achieve highly efficient expression and secretion of hLYZ in Pichia pastoris, multiple strategies including G418 sulfate screening, signal sequence optimization, vacuolar sorting receptor VPS10 disruption, and chaperones/transcription factors co‐expression were applied. The maximal enzyme activity of extracellular hLYZ in a shaking flask was 81,600 ± 5230 U mL−1, which was about five times of original strain. To further reduce the cost, the optimal medium RDMY was developed and the highest hLYZ activity reached 352,000 ± 16,696.5 U mL−1 in a 5 L fermenter.ConclusionThis research provides a very useful and cost‐effective approach for the hLYZ production in P. pastoris and can also be applied to the production of other recombinant proteins.

BACKGROUND Rare sugars have become promising ‘sugar alternatives’ because of their low calories and unique physiological functions. Among the family of rare sugars, d‐allulose is one of the sugars attracting interest. Ketose 3‐epimerases (KEase), including d‐tagatose 3‐epimerase (DTEase) and d‐allulose 3‐epimerase (DAEase), are mainly used for d‐allulose production. RESULTS In this study, a putative xylose isomerase from Caballeronia insecticola was characterized and identified as a novel DAEase. Caballeronia insecticola DAEase displayed prominent enzymatic properties, and 150 g L−1 d‐allulose was produced from 500 g L−1 d‐fructose in 45 min with a conversion rate of 30% and high productivity of 200 g L−1 h−1. Furthermore, DAEase was employed in a phosphorylation–dephosphorylation cascade reaction, which significantly increased the conversion rate of d‐allulose. Under optimized conditions, the conversion rate of d‐allulose was approximately 100% when the concentration of d‐fructose was 50 mmol L−1. CONCLUSION This research described a very beneficial and facile approach for d‐allulose production based on C. insecticola DAEase. © 2022 Society of Chemical Industry.

Rare sugars are monosaccharides with low natural abundance. They are structural isomers of dietary sugars, but hardly be metabolized. Here, we report that rare sugar l-sorbose induces apoptosis in various cancer cells. As a C-3 epimer of d-fructose, l-sorbose is internalized via the transporter GLUT5 and phosphorylated by ketohexokinase (KHK) to produce l-sorbose-1-phosphate (S-1-P). Cellular S-1-P inactivates the glycolytic enzyme hexokinase resulting in attenuated glycolysis. Consequently, mitochondrial function is impaired and reactive oxygen species are produced. Moreover, l-sorbose downregulates the transcription of KHK-A, a splicing variant of KHK. Since KHK-A is a positive inducer of antioxidation genes, the antioxidant defense mechanism in cancer cells can be attenuated by l-sorbose-treatment. Thus, l-sorbose performs multiple anticancer activities to induce cell apoptosis. In mouse xenograft models, l-sorbose enhances the effect of tumor chemotherapy in combination with other anticancer drugs. These results demonstrate l-sorbose as an attractive therapeutic reagent for cancer treatment.

The surface of the Saccharomyces cerevisiae spore wall exhibits a ridged appearance. The outermost layer of the spore wall is believed to be a dityrosine layer, which is primarily composed of a crosslinked dipeptide bisformyl dityrosine. The dityrosine layer is impervious to protease digestion; indeed, most of bisformyl dityrosine molecules remain in the spore after protease treatment. However, we find that the ridged structure is removed by protease treatment. Thus, a ridged structure is distinct from the dityrosine layer. By proteomic analysis of the spore wall-bound proteins, we found that hydrophilin proteins, including Sip18, its paralog Gre1, and Hsp12, are present in the spore wall. Mutant spores with defective hydrophilin genes exhibit functional and morphological defects in their spore wall, indicating that hydrophilin proteins are required for the proper organization of the ridged and proteinaceous structure. Previously, we found that RNA fragments were attached to the spore wall in a manner dependent on spore wall-bound proteins. Thus, the ridged structure also accommodates RNA fragments. Spore wall-bound RNA molecules function to protect spores from environmental stresses.