| First Author | Wang, K | Year | 2020 |
| Journal | PhD Thesis - The Chinese University of Hong Kong | Mgi Jnum | J:344979 |
| Mgi Id | MGI:7580872 | Citation | Wang, K (2020) Functional and Structural Studies of Cytosolic Sulfotransferase (Sult2a8) in Bile Acid and Energy Metabolism. PhD Thesis - The Chinese University of Hong Kong |
| abstractText | Cytosolic sulfotransferases (SULTs) are known as phase II conjugation enzymes catalyzing the transfer of a sulfonate group (SO3-) from the cofactor 3â- phosphoadenosine 5â-phosphosulfate (PAPS) to a hydroxyl or primary amine containing substrate. SULT-mediated sulfonation biotransforms various substrates including xenobiotics, hormones, neurotransmitters, and bile acids into polar compounds with higher water-solubility, and hence facilitates their excretion from the organism. Previously, we have discovered a new mouse SULT isoform preferentially sulfonating 7alpha-OH primary bile acids in vitro, suggesting the role of Sult2a8 in detoxification of bile acids, and further regulating bile acid metabolism. Human sulfonates bile acid via the 3alpha-OH group, while 7alpha-OH sulfonation is the major pathway for bile acid elimination in mouse. Existing evidences indicate that Sult2a8 is possibly the major SULT for regulation of bile acid metabolism via 7alpha-OH sulfonation. However, the molecular mechanism of Sult2a8-mediated 7alpha-OH sulfonation is still unclear. Moreover, increasing studies via exogenous bile acid treatment indicate that bile acids also function as signaling molecules to maintain energy homeostasis, implying that Sult2a8 may be involved in maintaining energy homeostasis through the bile acid sulfonation. However, direct evidence to support the relationship between endogenous bile acids and energy metabolic profiles in an animal model is still lacking. To explore the function of Sult2a8 in maintaining bile acids and energy metabolism in vivo, we attempted to create a Sult2a8 straight knockout (KO) mouse model by the targeted disruption of the exon 3 of the Sult2a8 gene. Intriguingly, homozygous KO embryonic lethality was found from the heterozygous (HT) intercrosses. Genotyping of the embryos from HT intercrosses revealed only limited KO embryos in the pre-implantation stages where no detectable mRNA expression of Sult2a8 was found, suggesting the Sult2a8 gene may not be involved in the embryonic lethality. Furthermore, the targeted disruption of one of the two Sult2a8 alleles in HT mutants resulted in approximately halving the hepatic Sult2a8 expression as well as sulfonation activities toward the 7alpha-OH bile acids. The HT mutants showed normal liver gross structure, but a concomitant increase of hepatic tauro-cholic acid and a decrease in plasma cholesterol level under energy deprivation. The association of a decreased hepatic SULT activity with a lower plasma cholesterol level suggests the ii regulatory role of SULT in cholesterol metabolism, and thus SULT is a potential therapeutic target for treating metabolic diseases. To investigate the molecular mechanism of the specific Sult2a8-mediated 7alpha-OH sulfonation towards bile acids, the crystal structure of Sult2a8 in complex with inactivated cofactor PAP and cholic acid was resolved. Structural studies revealed that Sult2a8 had a suitable substrate binding pocket for the 7alpha-OH sulfonation of bound cholic acid mediated by a non-conserved His48 residue. Double mutation of Lys44 and His48 residues abolished the Sult2a8-mediated sulfonation activities toward 7alpha-OH bile acid, suggesting that both Lys44 and the unique His48 are the catalytic residues. Together, these findings further support the role of Sult2a8 as the major SULT for 7alpha- OH sulfonation of bile acids as well as its potential application as a target for bile acid and energy metabolism in mice. ( https://repository.lib.cuhk.edu.hk/en/item/cuhk-2628086 ) |
