Distinct proteomes and allergen profiles appear across the life cycle stages of Alternaria alternata

Abstract

Alternaria alternata is associated with allergic respiratory diseases, which can be managed with allergen extract-based diagnostics and immunotherapy. It is not known how spores and hyphae contribute to allergen content. Commercial allergen extracts are manufactured by extracting proteins without separating the different forms of the fungus. To determine differences between spore and hyphae proteomes and how allergens are distributed in A. alternata. Data independent acquisition mass spectrometry to quantitatively compare the proteomes of asexual spores (non-germinating and germinating) with vegetative hyphae. We identified 4515 proteins in non-germinating spores, germinating spores and hyphae; most known allergens are more abundant in non-germinating spores. Comparing significant protein fold change differences between non-germinating spores and hyphae, 174 proteins were upregulated in non-germinating spores and 80 proteins in hyphae. Among the spore proteins are ones functionally involved in cell wall synthesis, responding to cellular stress, and maintaining redox balance and homeostasis. Comparing non-germinating and germinating spores, 25 proteins were upregulated in non-germinating spores and 54 in germinating spores. Among the proteins specific to germinating spores were proteases known to be virulence factors. One of the most abundant proteins in the spore proteome is sialidase, which has not been identified as an allergen but may be important in the pathogenicity of this fungus. Major allergen Alt a 1 is present at low levels in spores and hyphae and appears to be largely secreted into growth media. Spores and hyphae express overlapping but distinct proteomes. Most known allergens are found more abundantly in non-germinating spores.