Primary structure of the human M2 mitochondrial autoantigen of primary biliary cirrhosis: dihydrolipoamide acetyltransferase.

Abstract

Primary biliary cirrhosis is a chronic, destructive autoimmune liver disease of humans. Patient sera are characterized by a high frequency (greater than 95%) of autoantibodies to a Mr 70,000 mitochondrial antigen, a component of the M2 antigen complex. We have identified a human cDNA clone encoding the complete amino acid sequence of this autoantigen. The predicted structure has significant similarity with the dihydrolipoamide acetyltransferase (EC 2.3.1.12) of the Escherichia coli pyruvate dehydrogenase multienzyme complex. The human sequence preserves the Glu-Thr-Asp-Lys-Ala motif of the lipoyl-binding site and has two potential binding sites. Expressed fragments of the cDNA react strongly with sera from patients with primary biliary cirrhosis but not with sera from patients with autoimmune chronic active hepatitis or sera from healthy subjects.

Evidence for a locally driven mucosal response and the presence of mitochondrial antigens in saliva in primary biliary cirrhosis

“…3 In addition, recombinant proteins consisting of the 4 domains of human PDC-E2 were also used in this study. 17 Briefly, the EcoRI fragment (nucleotides 745-2,536) of the human PDC-E2 complementary DNA clone 3 was digested into 4 fragments with restriction endonucleases and subcloned into frame-matched derivatives of pBTA224 (fragment A, C, and D) and pGEX (fragment B).…”

“…Earlier studies from both our laboratory and others have shown that serum AMA react with a series of highly conserved mitochondrial proteins, in particular the 2-oxo acid dehydrogenase complexes, including the dihydrolipoamide acetyltransferase component of the pyruvate dehydrogenase complex E2 (PDC-E2), the branched chain 2-oxo acid dehydrogenase complex E2 (BCOADC-E2), and the 2-oxoglutarate dehydrogenase complex E2 (OGDC-E2). [2][3][4] The major serum autoantibody reactivity is directed against the 74-kd PDC-E2 protein; more than 90% of PBC patients have serum AMA directed against PDC-E2.…”

Diabetic sera react with the glutamic acid decarboxylase molecule in a dimeric-oligomeric form

“…Whilst there are some precedents for autoantigens existing as components of multimeric complexes, for example the pyruvate dehydrogenase complex, of M r 8 2 10 6 , for which the E 2 subunit is the major reactant with primary biliary cirrhosis sera [27], a requirement for a multimeric form of a molecule for autoantigenic reactivity is exceptional. One precedent is the proliferating cell nuclear antigen (PCNA) which appears to require a trimeric structure for autoantigenic reactivity, since recombinant proteins that contain mutations or deletions preventing formation of trimers are non-reactive with autoantibodies [28].…”

Characterization and epitope mapping of human monoclonal antibodies to PDC-E2, the immunodominant autoantigen of primary biliary cirrhosis

“…Among these autoantigens, human PDC-E2 has been cloned, sequenced and expressed [8,9]. Previous studies of epitope mapping have relied on whole sera and have suggested that the immunodominant epitope lies within the inner lipoyl domain of the molecule and may include a large conformational component [9,10].…”