Use of Domain-Deletion Mutants to Locate Lutheran Blood Group Antigens to Each of the Five Immunoglobulin Superfamily Domains of the Lutheran Glycoprotein: Elucidation of the Molecular Basis of the Lua/Lub and the Aua/Aub Polymorphisms

Abstract

AbstractLutheran glycoprotein (Lu gp) has five predicted immunoglobulin superfamily (IgSF ) domains. K562 cells were transfected with Lu cDNA and tested by flow cytometry with monoclonal antibodies and Lu blood group antisera. The results confirmed the identity of Lu cDNA. Deletion mutants lacking the regions encoding one or more IgSF domains were made by inverse polymerase chain reaction (PCR), expressed in K562 cells, and tested with the same antibodies. The Lub and Lu5 antigens and the epitope recognized by monoclonal antibody BRIC 224 were mapped to the first, N-terminal, IgSF domain. Lu4 and Lu8 were mapped to domain 2; Lu20 to domain 3; Lu7 and BRIC 221 epitope to domain 4, and Lu13 and Aub to domain 5. The organization of the LU gene was determined. The region encoding the open reading frame is arranged in 15 exons extending over ≈11 kb on chromosome 19q13.2. The Lua/Lub and Aua/Aub blood group polymorphisms were studied using genomic DNA from typed blood donors. The Lua mutation is a base change in exon 3 (G252 to A) encoding an Arg77 (Lub) to His (Lua) change on the CFG face of domain 1. The Aua/Aub polymorphism is an A1637 to G substitution in exon 12 encoding a Thr539 (Aua) to Ala (Aub) change on the G strand of domain 5.