Influence Of UGT Homo-and Hetero-oligomer Formation On Enzymatic Activity And Its Mechanism

UDP-glucuronosyltransferases (UGTs) are important drug phase II enzymes. They catalyze the formation of β-D-glucuronides using UDP-glucuronic acid and acceptor substrates such as drugs, steroids, bile acids, xenobiotics, and dietary nutrients. Thus the polarity of these substrates was increased, and this benefits the excretion of them. Single nucleotide polymorphisms (SNPs) broadly exist in UGT genes, causing changes in metabolism and disease (e.g. Gilbert syndrome is caused by some mutations in UGT1A1). Interaction between UGT1A and UGT2B members had been reported frequently, and they changed in activity with oligomer formation. It has been reported a lot that when coexpressed with mutant enzymes, total activity is lower than single expression of either enzyme. It can prove that their interation changed structure of both of them. Similar phenomenon exists in human body, so research on the interaction mechanism between UGT*N and UGT*N is important. In this paper, analysis was carried on UGT1A1and one splice variant, UGT1A9and three functional mutants, and UGT2B7and three functional mutants.Recombinant UGT*N marked with CFP or YFP were homo or hetero expressed with Bac-to-Bac expression system. Fluorescence resonance energy transfer (FRET) and Co-IP were used to determine whether oligomer was formed. The amount of expressed enzymes was estimated with Western blot and the relative activity was calculated. By analyzing these data, according to the truncated enV2interacting widely with N-terminal and C-terminal, UGTIAlb lost enzyme activity; Interaction between UGT1A9*1and UGT1A9*1involved in hydrophobic interaction and hydrogen bond; interaction face between UGT1A1and UGT2B7may be located on the cosurface comprised of Ca5, Nα2-Nβ3and Na6-Nβ7of UGT2B7*1.