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Characterization of the autoantibody responses to recombinant E3 binding protein (protein X) of pyruvate dehydrogenase in primary biliary cirrhosis

Lookup NU author(s): Dr Jeremy Palmer, Professor David Jones, Professor Janet Quinn, Anna McHugh, Emeritus Professor Steve Yeaman


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Autoantibodies to the pyruvate dehydrogenase complex (PDC) are present in the serum of more than 95% of patients with primary biliary cirrhosis (PBC), the major epitope being the inner lipoyl domain of the E2 component. Immunoblotting suggests a similar prevalence of antibodies to a tightly associated lipoic acid-containing protein, E3 binding protein (E3BP). Attempts to resolve E3BP from E2 have been unsuccessful, restricting study of the nature and significance of antibody responses to the individual proteins. In particular, it is unclear (1) whether there is true cross-reactivity between E3BP and E2 and, if so, which is the originating response and (2) whether autoantibodies preferentially bind a lipoylated epitope on E3BP as is the case with PDC-E2. In this study, complementary DNAs encoding rE2, full- length rE3BP, its single lipoyl domain (rLip), and core domain (rE3BPCore) were cloned, and the proteins were expressed in Escherichia coli. Sera from 47 PBC patients were studied by immunoblotting and enzyme-linked immunosorbent assay (ELISA) against rE2, rE3BP, rE3BPCore, and both unlipoylated (U) and lipoylated (L) rLip. All sera were reactive by ELISA to some degree with all recombinant proteins except rE3BPCore, to which only 6 of 47 showed any reactivity. Significant correlations (P < .0001) were observed when comparing absorbance values for rE3BP with both rLip (U) (r = 0.793) and (L) (r = 0.963). The mean absorbance for rLip (U, 0.26 ± 0.05) was, however, significantly lower than the absorbance for rLip (L) (0.78 ± 0.12; P < .0001). After probing by immunoblotting and elution of antibodies from rE2 and rE3BP, subsequent reprobing against the components in whole PDC revealed true cross-reactivity. In summary, the response to E3BP is primarily directed against the lipoylated domain of the protein. It still remains unclear, however, whether the initial breakdown of tolerance is to E2 or E3BP.

Publication metadata

Author(s): Palmer JM, Jones DEJ, Quinn J, McHugh A, Yeaman SJ

Publication type: Article

Publication status: Published

Journal: Hepatology

Year: 1999

Volume: 30

Issue: 1

Pages: 21-26

Print publication date: 01/07/1999

ISSN (print): 0270-9139

ISSN (electronic): 1527-3350

Publisher: John Wiley & Sons, Inc.


DOI: 10.1002/hep.510300106

PubMed id: 10385634


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