Characterization of human antigenic proteins SchS21 and SchS34 from Stachybotrys chartarum.

BACKGROUND

SchS21 and SchS34 are proteins from Stachybotrys chartarum sensu latto that are antigenic in goats, mice and humans. Monoclonal antibodies to these proteins react with spores of S. chartarum and S. chlorohalonata but do not cross-react with a diverse taxonomic and ecological array of other fungi.

METHODS

Based on partial sequences of the 21- and 34-kDa proteins, obtained from tandem mass spectra and Edman degradation, degenerate primers were designed for touchdown PCR and the resulting amplicons were sequenced. Subsequently, inverse-PCR was used to obtain genomic DNA sequences encoding SchS21 and SchS34. RT-PCR products were sequenced to predict the mature protein sequences of SchS21 and SchS34. Based on the speculation that SchS21 protein was a DNase, the enzymatic properties were investigated.

RESULTS

Sequences of 435 and 666 bp in length were obtained from SchS21 and SchS34 cDNAs. The SchS21 open reading frame encodes a mature protein of 144 amino acids, while that of SchS34 is 221 amino acids in length. SchS21 is a secretory, alkaline, Mg-dependent exodeoxyribonuclease, while SchS34 is a secretory protein of unknown function. His-tagged forms of the mature SchS21 and SchS34 proteins were separately overexpressed in Escherichia coli and purified using Ni-NTA columns (0.5 mg/l yield).

CONCLUSIONS

Based on Western blots, the expressed proteins were similar in molecular weight and bound to the respective monoclonal antibodies to SchS21 and SchS34 proteins from S. chartarum. Interactions with human sera IgE confirmed the expressed forms of SchS21 and SchS34 as naturally occurring allergens.