Background: The Gerbich-related Lsa blood group antigen (Ge6) resides on the higher-molecular-weight forms of glycophorin C (GPC) and glycophorin D (GPD). Southern blot analysis has previously revealed an additional GPC exon 3 insert in the genomic DNA from an Ls(a+) individual.
Study design and methods: To confirm the duplication of exon 3 in the GPC mRNA, total RNA prepared from the Epstein-Barr virus-transformed lymphocytes of an Ls(a+) individual was used in the synthesis of first-strand cDNA. The first-strand cDNA served as a template for the amplification of GPC-related DNA by polymerase chain reaction. After subcloning, the polymerase chain reaction cDNA was sequenced with a kit. Hemagglutination inhibition of anti-Lsa sera with synthetic peptides was performed to identify the location of Lsa on the GPC.Lsa protein.
Results: Sequencing the GPC.Lsa cDNA showed an insert of 84 nucleotides, which corresponds to the entire sequence of exon 3 in the GPC gene (GYPC). Since the exon 3-duplicated exon 3 boundary of GYPC.Lsa encodes a novel amino acid sequence on GPC.Lsa and GPD.Lsa, synthetic peptides consisting of the amino acids flanking this junction were used to determine the amino acid sequence that is essential for expression of Lsa. The peptide DIVVIA/EPDPG was noninhibitory, while peptides with the sequence TPTIMDIVVIA/EPDPG or SPSVLDIVVIA/EPDPG inhibited anti-Lsa reactivity.
Conclusion: Lsa is located within the sequence of amino acids encoded by the nucleotides at the exon 3-duplicated exon 3 boundary, and the conformation of this peptide sequence is important for recognition of Lsa by human anti-Lsa.