INTRODUCTION
M2 autoantigen is a key mark of antimitochondrial autoantibodies (AMA), a typical serological feature in patients suffering from primary biliary cirrhosis (PBC) which is a serious autoimmune liver disease accompanied by damage to intrahepatic bile ducts. Molecular definition of the M2 antigen has displayed it as no less than 3 separate target proteins. The M2 role is like the so-called E2 subunits (or dihydrolipoamide transferases) of different mitochondrial dehydrogenase complexes:
*pyruvate dehydrogenase complex.
*branched chain 2-oxo-acid dehydrogenase complex.
*2-oxoglutarate dehydrogenase complex.
Biochemically, these complexes catalyze the oxidative decarboxylation of various alpha-keto-acid substrates and systematically engage with a prosthetic lipoamide group; they are situated in the mitochondrial matrix in association with the inner membrane. The most well-known reactivity of AMA positive PBC sera is against PDC-E2. Some patients have AMA which reacts with PDC-E2 alone (95%), but most patients also show reactivity against OGDC-E2 (39-88%) and/or BCOADC-E2 (53-55%). Actually, patients can be found with reactivity only against OGDC-E2 and/or BCOADC-E2 and no PDC-E2 autoantibodies. These patients will be overlooked in assays based on natural source-derived, predominantly PDC-E2-containing M2 antigen preparations.
DESCRIPTION
Recombinant antigen for solid (ELISA) and fluid phase diagnostic assays. Mixture of E2/dihydrolipamide acyltransferase-subunits from 3 mitochondrial protein complexes: pyruvate dehydrogenase complex (PDC-E2) having a molecular mass of 60,630 Dalton (pI 5.8); 2-oxo-glutarate dehydrogenase complex (OGDC-E2) having a molecular mass of 42,301 Dalton (pI 6.3); branched chain 2-oxo-acid dehydrogenase complex (BCOADCE2) having a molecular mass of 47,321 Dalton (pI 6.5). Mixture contains equal mass of each protein component. cDNAs coding for the mature forms of the human PDC-E2, OGDC-E2 and BCOADC-E2 proteins individually fused to a hexa-histidine purification tag.
