Complete primary structure of a Lolium perenne (perennial rye grass) pollen allergen, Lol p III: comparison with known Lol p I and II sequences

The complete amino acid sequence of a Lolium perenne (rye grass) pollen allergen, Lol p III, determined by the automated Edman degradation of the protein and its selected fragments, is reported in this paper. Cleavage by enzymatic and chemical techniques established unambiguously the sequence for this 97-residue protein (Mr = 10,909), which lacks cysteine and shows no evidence of glycosylation. The sequence of Lol p III is very similar to that of another L. perenne allergen, Lol p II, which was sequenced recently; of the 97 positions in the two proteins, 57 are occupied by identical amino acids (59% identity). In addition, both allergens share a similar structure with an antibody-binding fragment of a third L. perenne allergen, Lol p I. Since human antibody responsiveness to all these three allergens is associated with HLA-DR3, and since the structure common to the three molecules shows high degrees of amphipathicity in Lol p II and III, we speculate that this common segment in the three molecules might contain or contribute to the respectively Ia/T-cell sites.