In order to obtain special lactic acid bacteria with potent uric acid-lowering activity, this study screened lactic acid bacterial strains for their ability to degrade inosine and guanosine by high performance liquid chromatography (HPLC). The strain LB1lac20 was found to give the highest degradation rate of inosine (91.19%) and guanosine (89.67%). By sequence alignment of 16S rRNA gene using the Basic Local Alignment Search Tool (BLAST), LB1lac20 was identified as Lactobacillus brevis. To evaluate its uric acid-lowering potential, an in vitro model was established by the uric acid production method and used to analyze the inhibitory effect of LB1lac20 on xanthine oxidase. The results showed that the activity of xanthine oxidase was 21.27% and 19.60% inhibited by the live suspension and intracellular extract of LB1lac20, respectively (P < 0.05). To sum up, L. brevis LB1lac20 may set the stage for the development of drugs for the prevention and treatment of hyperuricemia.

In this study, through promoter optimization and host screening, an SplB expression vector with His-tag at the C-terminal was constructed, and SplB was successfully expressed in Bacillus subtilis. The enzymatic properties of the purified recombinant SplB protease were studied, and the application of recombinant SplB protease in the cleavage of recombinant protein Prx with a tag was explored. The results showed that using B. subtilis ATCC6051Δ10 as the host, the recombinant expression activity of SplB mediated by promoter P₄₃ was the highest (10.24 U/mL). The recombinant SplB was purified by affinity chromatography and its enzymatic properties were studied. The optimum temperature was 40 ℃, the optimum pH was 8.5, and the purified SplB had good temperature and pH stability. Low concentrations of Co²⁺ promoted the activity of SplB, while low concentrations of Mg²⁺ and K⁺ did not affect its activity; low concentrations of Cu²⁺, Zn²⁺ and Ni⁺ inhibited the activity of SplB, and sodium dodecyl sulfate (SDS) greatly inhibited the enzyme activity of recombinant SplB. The recombinant SplB protease could concentration-dependently cleave the WELQ peptide tag on the recombinant protein Prx. This study provides support for optimizing the recombinant expression of SplB and its application in the fields of food and medicine.

Clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9’s main element Cas9 protein is generally expressed by Escherichia coli, but in the process of expression and purification, Cas9 protein is prone to problems such as the formation of insoluble inclusion bodies, high endotoxin content, incorrect protein folding due to too large protein molecules, and low yield. This study aimed to achieve efficient soluble expression of Streptococcus pyogenes Cas9 (SpCas9) protein in E. coli for the purpose of promoting its application and popularizing gene editing technology. The solubility-enhancing tag GB1 was applied to improve the expression level and solubility of Cas9 protein, and a multiple promoter strategy was used to further improve the expression level of Cas9 protein. As a result, the expression of Cas9 protein was increased by 3.52 times. In vitro enzymatic digestion analysis showed that the functional activity of Cas9 protein was not affected by fusion with GB1. Furthermore, a ribonucleoprotein (RNP) complex was assembled and transformed into the host Aspergillus niger, so that the pyrG gene was successfully destroyed.