Division of Pharmaceutical Cell Biology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan; Laboratory of Hygienic Chemistry, Faculty of Pharmaceutical Sciences, Sojo University, Kumamoto, Japan.
Division of Pharmaceutical Cell Biology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
Drug Metab Pharmacokinet. 2020 Oct;35(5):466-474. doi: 10.1016/j.dmpk.2020.07.006. Epub 2020 Aug 14.
UDP-Glucuronosyltransferase (UGT) is a type I membrane protein localized to the endoplasmic reticulum (ER). UGT has a di-lysine motif (KKXX/KXKXX) in its cytoplasmic domain, which is defined as an ER retention signal. However, our previous study has revealed that UGT2B7, one of the major UGT isoform in human, localizes to the ER in a manner that is independent of this motif. In this study, we focused on another UGT isoform, UGT1A9, and investigated the role of the di-lysine motif in its ER localization, glucuronidation activity, and homo-oligomer formation. Immunofluorescence microscopy indicated that the cytoplasmic domain of UGT1A9 functioned as an ER retention signal in a chimeric protein with CD4, but UGT1A9 itself could localize to the ER in a di-lysine motif-independent manner. In addition, UGT1A9 formed homo-oligomers in the absence of the motif. However, deletion of the di-lysine motif or substitution of lysines in the motif for alanines, severely impaired glucuronidation activity of UGT1A9. This is the first study that re-defines the cytoplasmic di-lysine motif of UGT as an essential peptide for retaining glucuronidation capacity.
UDP-葡萄糖醛酸基转移酶 (UGT) 是一种定位于内质网 (ER) 的 I 型膜蛋白。UGT 在其细胞质结构域中具有二赖氨酸基序 (KKXX/KXKXX)，该基序被定义为 ER 保留信号。然而，我们之前的研究表明，UGT2B7 是人类主要的 UGT 同工酶之一，其在 ER 中的定位方式不依赖于该基序。在本研究中，我们专注于另一种 UGT 同工酶 UGT1A9，并研究了二赖氨酸基序在其 ER 定位、葡萄糖醛酸化活性和同型寡聚体形成中的作用。免疫荧光显微镜分析表明，UGT1A9 的细胞质结构域在与 CD4 融合的嵌合蛋白中作为 ER 保留信号发挥作用，但 UGT1A9 本身可以以不依赖于二赖氨酸基序的方式定位于 ER。此外，UGT1A9 在没有该基序的情况下形成同型寡聚体。然而，删除二赖氨酸基序或用丙氨酸取代该基序中的赖氨酸，严重损害了 UGT1A9 的葡萄糖醛酸化活性。这是第一项重新定义 UGT 细胞质中二赖氨酸基序作为保留葡萄糖醛酸化能力的必需肽的研究。
