ABSTRACT
Human glutamate decarboxylase 65(hGAD65) is an enzyme that catalyzes the transformation of L-glutamic acid into ?-aminobutyric acid.It has been found that Type 1 diabetes mellitus(T1DM)is an autoimmune disease,in which pancreatic islet ?-cells are destroyed due to immune response mediated by autoantigen.hGAD65 is considered as a key autoantigen of the autoimmune response,so anti-hGAD65 antibody(hGAD65-Ab) is the most effective and specific immune marker for T1DM diagnosis,and hGAD65 can be used to detect hGAD65-Ab in serum of T1DM patients.The hGAD65 gene was cloned into pET32a(+),then the recombinant plasmid with hGAD65 was transformed into E.coli BL21(DE3) and expressed by IPTG induction.The fusion protein containing thioredox,hexahistidine and hGAD65(Trx-hGAD65) was mostly insoluble,but the band of soluble Trx-hGAD65 could also be detected by SDS-PAGE,and it was a great improvement compared with the results reported.Trx-hGAD65 was isolated from lysate and purified by immobilized metal ion affinity chromatography(IMAC).After enterokinase digestion and IMAC purification,hGAD65 with high purity was obtained.Detection of thin-layer chromatography(TLC) showed that both Trx-hGAD65 and hGAD65 had enzymatic activity,whereas Trx-hGAD65 had better stability.Furthermore,it was confirmed that Trx-hGAD65 was able to conjugate with hGAD65-Ab in the serum of T1DM patients by ELISA assay.In conclusion,Trx-hGAD65 instead of hGAD65 can be used for T1DM diagnosis,and its application in prophylaxis and therapy of T1DM is expectable.