Characterization of the Aspergillus nidulans aspnd1 gene demonstrates that the ASPND1 antigen, which it encodes, and several Aspergillus fumigatus immunodominant antigens belong to the same family

Abstract

For the first time, an immunodominant Aspergillus nidulans antigen (ASPND1) consistently reactive with serum samples from aspergilloma patients has been purified and characterized, and its coding gene (aspnd1) has been cloned and sequenced. ASPND1 is a glycoprotein with four N-glycosidically-bound sugar chains (around 2.1 kDa each) which are not necessary for reactivity with immune human sera. The polypeptide part is synthesized as a 277-amino-acid precursor of 30.6 kDa that after cleavage of a putative signal peptide of 16 amino acids, affords a mature protein of 261 amino acids with a molecular mass of 29 kDa and a pI of 4.24 (as deduced from the sequence). The ASPND1 protein is 53.1% identical to the AspfII allergen from Aspergillus fumigatus and 48% identical to an unpublished Candida albicans antigen. All of the cysteine residues and most of the glycosylation sites are perfectly conserved in the three proteins, suggesting a similar but yet unknown function. Analysis of the primary structure of the ASPND1 coding gene (aspnd1) has allowed the establishment of a clear relationship between several previously reported A. fumigatus and A. nidulans immunodominant antigens.