Amino acid sequence of an alpha-delta-glycophorin hybrid. A structure reciprocal to Sta delta-alpha-glycophorin hybrid

Abstract

In this report we examine the primary sequence of a variant glycophorin obtained from erythrocytes of an individual who exhibits an unusual MNSs blood group phenotype. We show that this protein is a hybrid molecule constructed from sequences of alpha- and delta-glycophorins (glycophorins A and B) in a alpha-delta arrangement. Serological typing revealed that the donor's phenotype was M+N+S+s+U+; yet his erythrocytes reacted with some but not all examples of anti-S antisera. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed a variant glycophorin band, and immunoblotting and reaction with N-glycanase suggested that its amino terminus resembled that of M-alpha-glycophorin but that its carboxyl terminus did not. A preparation highly enriched in the variant was obtained and used to generate peptide fragments for sequencing. The sequence revealed that the variant was a hybrid molecule whose amino terminus corresponded to M-alpha-glycophorin and whose carboxyl terminus corresponded to S-delta-glycophorin. CNBr cleavage of the variant glycophorin yielded four peptides. The sequence of the amino-terminal CNBr peptide (residues 1-8) was identical to the amino-terminal octapeptide of M-alpha-glycophorin. The proceeding peptide (residues 9-61) contained a segment identical to residues 9-58 of alpha glycophorin, but its carboxyl-terminal sequence had the Gly-Glu-Met sequence from S-delta-glycophorin (residues 27-29). The other two peptides, insoluble in aqueous solutions, contained highly hydrophobic sequences, identical to residues 30-52 and 53-68 of delta-glycophorin. Sequences of overlapping peptides generated by trypsin and V8 protease confirmed the hybrid nature of the variant glycophorin: residues 1-58 were identical to residues 1-58 of M-alpha-glycophorin, and residues 59-100 were entirely identical to residues 27-68 of S-delta-glycophorin. The variant glycophorin is expected to have 4 additional residues at its carboxyl terminus that correspond to the carboxyl-terminal residues 69-72 of delta-glycophorin. The amino acid sequence arrangement of the variant alpha-delta-glycophorin is an exact reciprocal of that found in another hybrid glycophorin, Sta, that is a delta-alpha hybrid. We propose that the two hybrid glycophorins represent the two possible products resulting from a reciprocal recombination event.