Localization of a Pernicious Anaemia Autoantibody Epitope on the a'-Subunit of Human H,K-Adenosine Triphosphatase

Abstract

Song Y-H, Ma J-Y, Mårdh S, Liu T, Sjostrand SE, Rask L, Borch K, Huang G-C, Barnett P, McGregor AM. Banga JP. Localization of a pernicious anaemia autoantibody epitope on the α-subunit of human H.K-adenosine triphosphatase. Scand J Gastroenterol 1994;29:122-127.

Four cDNA fragments encoding different portions of the α-subunit of human H,K-adenosine triphosphatase (ATPase) were amplified by means of the polymerase chain reaction technique, ligated into the plasmid pGEX-2T, and expressed as glutathione S-transferase fusion proteins in Escherichia coli. The fragments A (residues 163-313), Ba (residues 360-797), Bb (residues 526-797), and C (residues 822-1031) together encompass 77% of the a'-Subunit and cover most of its cytosolic part. The reactivities of autoantibodies in the sera from patients with pernicious anaemia with the recombinant fusion proteins were analysed by immunoblotting. One autoantigenic epitope was found in the NH₂-terminal part of the Ba fragment–that is, between residues 360 and 525. No epitope was detected in the other fragments. The Ba fragment was cleaved off from the glutathione S-transferase fusion protein by the action of thrombin and was then further purified. By means of enzyme-linked immunosorbent assay, 28 of 42 sera (67%) from patients with pernicious anaemia were positive against the purified Ba fragment. The present results provide a final proof that the human H,K-ATPase o–subunit is a major autoantigen in the parietal cell and that the major epitope is located between residues 360 to 525 on the cytosolic side of the secretory membrane.

Key Words:

• Autoantigenic epitope
• pernicious anaemia
• recombinant H,K-ATPase α-Subunit