The N-terminal of human UGT1A6 is on the outside, as evidenced by ELISA with autoantibody in autoimmune hepatitis sera.
Sera from AIH (autoimmune hepatitis) type 2 patients contain an autoantibody against the UGT1A subtype, called anti-LKM3. Previously, we reported that sera in AIH type 1 patients contained autoantibodies against drug-metabolizing enzymes (Shinoda et al. (2004) Autoimmunity, 37, 473). In this report, we showed that AIH-1 sera did not react with some peptides in the C-terminal half of the UGT1A subtype but reacted with a peptide P1(33-42) among several common peptides in the N-terminal half of the UGT1A subtype. This result suggests that the P1 site (33-42) presents on the outside of the UGT1A molecule to be recognized by lymphocytes of the immune system to produce an autoantibody. To detect a key recognition site on peptide P1(33-42), we studied the reactivity of two peptides, M1(28-37) and M2(38-47), containing the N-terminal and C-terminal half of peptide P1. Peptide M2 did not react with AIH-1 serum but peptide M1 did. Thus, the common peptide sequence 33-37 in the positive peptide M1(28-37) and P1(33-42) is a key recognition sequence. Next, we studied the reactivity of some other synthetic peptides, in which some amino acids in the sequence 33-37 in peptide M1 changed to Ala. The peptides changing to Ala (PQ33-34AA) or (DGS35-37AAA) did not react with AIH-1 sera. Meanwhile, these AIH sera did not inhibit the glucuronidation of p-nitrophenol by UGT1A6, suggesting that the key sequence 33-37 might not be contained in active sites of glucuronidation by UGT1A6. In conclusion, sera from AIH-1 patients reacted with the amino acids in the sequence 33-37 (PQDGS) of the N-terminal of UGT1A6.
Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan.
Hitomi
H
Mori
Masakazu
M
Shinoda
Takaharu
T
Mizutani
D000595:Amino Acid Sequence; D001323:Autoantibodies / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D020719:Glucuronides / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000276:immunology*; D019693:Hepatitis, Autoimmune / Q000276:immunology*; D006801:Humans; D008214:Lymphocytes / Q000276:immunology; D008875:Middle Aged; D009596:Nitrophenols / Q000378:metabolism; D010455:Peptides / Q000737:chemistry
D001323:Autoantibodies; D020719:Glucuronides; D009596:Nitrophenols; D010455:Peptides; C110655:UDP-glucuronosyltransferase, UGT1A6; D014453:Glucuronosyltransferase; C024836:4-nitrophenol