Résumé
@#Objective To express insulin-degrading enzyme(IDE)mutant T142A in prokaryotic cells and detect its activity.Methods According to the results of multi-sequence alignment and IDE substrate co-crystal structure,an active residue in β6-strand structure of IDE were predicted.The recombinant plasmid ppSUMO-T142A,with the site mutation of threonine 142 to alanine,was constructed by point mutation technique and expressed by E.coli prokaryotic expression system.After purification by nickel ion column affinity chromatography,ion exchange chromatography and gel filtration chromatography,the mutant T142A was obtained and determined for the activity by fluorescence method.Results IDE amino acid sequence is highly conserved among 16 species.T142 directly participates in substrate binding,interacts with substrate cleavage sites,and is close to important structures such as catalytic active sites and door-subdomains.The mutation of recombinant plasmid ppSUMO-T142A was proved to be correct by sequencing.The expressed fusion protein His-SUMO-T142A was mainly existed in soluble form in the supernatant at a concentration of 18 mg/mL,with a relative molecular mass of about 131 000;After three steps of purification,the purity of mutant T142A reached 86%.The maximum reaction rate(V_(max))of T142A catalytic degradation of fluorescent substrate V was 501.06 min~(-1) and the Michaelis constant(K_m) was 9.01μmol/L.Compared with wild-type IDE(V_(max) was 2 814.32 min~(-1),K_m was 11.93μmol/L),the activity of T142A decreased significantly.Conclusion The activity of IDE mutant T142A expressed in this study greatly decreases,while T142 is an important residue for IDE to play its enzymatic function,which provides an experimental basis for the development of new IDE activity regulatory molecules.
Résumé
Objective: To observe the effect of Hei Xiaoyaosan on expressions of β-amyloid 1-42 peptide(Aβ1-42),glycogen synthase kinase-3β(GSK-3β),neprilysin(NEP),insulin-degrading enzyme(IDE) in the hippocampus area of Alzheimer's dementia mice. Method: After weighing, 42 APP/PSI bivalent transgenic mice were randomly divided into 4 groups:10 mice in the model group, 10 mice in the positive drug control group, 11 mice in the high-dose Hei Xiaoyaosan group, and 11 mice in the low-dose Hei Xiaoyaosan group; 10 wild C57BL/6J mice of the same age and strain were used for negative control group. Drugs were administered to mice by gavage once a day for 12 weeks. Then the behavior of all the mice were detected by Morris water maze, the morphological changes in hippocampal neurons were observed by hematoxylineosin(HE) staining, the expressions of Aβ1-42, GSK-3β, NEP and IDE proteins in hippocampus were detected by immunohistochemistry. Result: After 3 months of treatment, compared with negative control groups, the average escaping latency periods prolonged significantly, and the number of cross-platform was decreased significantly in model group (Pβ1-42 and GSK-3β proteins in model mice hippocampus were significantly increased (PPPβ1-42 and GSK-3β proteins in the hippocampus of drug groups were significantly decreased (PPPConclusion: Hei Xiaoyaosan can significantly improve the learning and memory abilities of AD mice, which may be related to the reduction of cognitive impairment in AD mice by regulating abnormal deposition and degradating Aβ in the hippocampus.