The Importance of Local Chemical Structure for Chemical Metabolism by Human Uridine 5‘-Diphosphate−Glucuronosyltransferase

Abstract

The uridine 5'-diphosphate- (UDP-)glucuronosyltransferase (UGT) family of enzymes catalyzes the conjugation of chemicals containing a suitable nucleophilic atom with glucuronic acid. Despite the importance of glucuronidation as an elimination and detoxification mechanism for drugs, environmental chemicals, and endogenous compounds, the structural features of substrates that confer isoform selectivity are poorly understood. The relationship between the local molecular structure of nucleophilic atoms of chemicals and the ability of UGT isoforms to glucuronidate the nucleophilic atoms was investigated here. The proximity of an aromatic ring to the nucleophilic atom was highly associated with a greater likelihood of glucuronidation by most UGT isoforms. Similarly, most UGT isoforms were found to have a statistically significant preference for oxygen over nitrogen as the nucleophilic atom. The converse was established only for UGT1A4. Naïve Bayes models were trained to predict the site of glucuronidation for eight UGT isoforms on the basis of the partial charge and Fukui function of the nucleophilic atom and whether an aromatic ring was attached to the nucleophilic atom. On average, the cross-validated sensitivity and specificity of the models were approximately 75-80%. For all but UGT2B7, the area under the receiver operating characteristics curve of the model was greater than 0.8, indicating strong predictive ability. A chemical diversity analysis of the currently available data indicates bias toward chemicals containing phenolic groups, and it is likely that the availability of chemical data sets with greater diversity will facilitate further insights into the structural features of substrates that confer enzyme selectivity.