CDNA CLONING AND SEQUENCING REVEAL THE MAJOR HORSE ALLERGEN EQU C1 TOBE A GLYCOPROTEIN MEMBER OF THE LIPOCALIN SUPERFAMILY

The gene encoding the major horse allergen, designated Equus caballus allergen 1 (Equ c1), was cloned from total cDNA of sublingual salivary glands by reverse transcription-polymerase chain reaction using synth etic degenerate oligonucleotides deduced from N-terminal and internal peptide sequences of the glycosylated hair dandruff protein. A recombi nant form of the protein, with a polyhistidine tail, was expressed in Escherichia coli and purified by immobilized metal affinity chromatogr aphy. The recombinant protein is able to induce a passive cutaneous an aphylaxis reaction in rat, and it behaves similarly to the native Equ c1 in several immunological tests with allergic patients' IgE antibodi es, mouse monoclonal antibodies, or rabbit polyclonal IgG antibodies. Amino acid sequence identity of 49-51% with rodent urinary proteins fr om mice and rats suggests that Equ c1 is a new member of the lipocalin superfamily of hydrophobic ligand-binding proteins that includes seve ral other major allergens. An RNA blot analysis demonstrates the expre ssion of mRNA Equ c1 in liver and in sublingual and submaxillary saliv ary glands.