A novel structural mechanism for redox regulation of uridine phosphorylase 2 activity

Abstract

Uridine phosphorylase (UPP) catalyzes the reversible conversion of uridine to uracil and ribose-1-phosphate and plays an important pharmacological role in activating fluoropyrimidine nucleoside chemotherapeutic agents such as 5-fluorouracil and capecitabine. Most vertebrate animals, including humans, possess two homologues of this enzyme (UPP1 & UPP2), of which UPP1 has been more thoroughly studied and is better characterized. Here, we report two crystallographic structures of human UPP2 (hUPP2) in distinctly active and inactive conformations. These structures reveal that a conditional intramolecular disulfide bridge can form within the protein that dislocates a critical phosphate-coordinating arginine residue (R100) away from the active site, disabling the enzyme. In vitro activity measurements on both recombinant hUPP2 and native mouse UPP2 confirm the redox sensitivity of this enzyme, in contrast to UPP1. Sequence analysis shows that this feature is conserved among UPP2 homologues and lacking in all UPP1 proteins due to the absence of a necessary cysteine residue. The state of the disulfide bridge has further structural consequences for one face of the enzyme that suggest UPP2 may have additional functions in sensing and initiating cellular responses to oxidative stress. The molecular details surrounding these dynamic aspects of hUPP2 structure and regulation provide new insights as to how novel inhibitors of this protein may be developed with improved specificity and affinity. As uridine is emerging as a promising protective compound in neuro-degenerative diseases, including Alzheimer’s and Parkinson’s, understanding the regulatory mechanisms underlying UPP control of uridine concentration is key to improving clinical outcomes in these illnesses.

Genome-wide association study identifies novel susceptibility loci for migraine in Han Chinese resided in Taiwan

“…Uridine, a substrate for the synthesis of DNA, RNA, membrane constituents, and glycosylation, is a major pyrimidine nucleoside taken up by the brain. UPP2 is important in sensing and initiating cellular responses to oxidative stress (42). These findings are consistent with the proposed mechanisms in a previous meta-analysis of migraine GWASs (10).…”

Relative mRNA expression of prostate-derived E-twenty-six factor and E-twenty-six variant 4 transcription factors, and of uridine phosphorylase-1 and thymidine phosphorylase enzymes, in benign and malignant prostatic tissue

“…In the prostatic carcinoma tissues, no correlation was found between the relative expression levels of TP and Gleason score or TNM classification, which is consistent with the majority of previous studies (55). In immunohistochemical studies of colorectal cancer, the expression of TP in stromal cells has been associated with a good prognosis; however, in breast cancer, increased TP expression was associated with a poor prognosis (56-58) It is likely that the expression of this enzyme varies according to the type of tissue, such as in tumor tissues infiltrated by macrophages, which exhibit an overexpression of TP (59).…”

Chronic Uridine Administration Induces Fatty Liver and Pre-Diabetic Conditions in Mice

“…However, UPase1 is ubiquitously present in every tissue while UPase2 is a liver-specific protein [ 34 ]. Furthermore, the active site of UPase2 has a disulfide bridge between two cysteine residues, which is absent in UPase1 [ 37 ]. Consequently, enzymatic activity of UPase2, but not UPase1, is sensitive to redox regulation.…”