Functional Study Of The Erg4 Gene Associated With Aspergillus Fumigatus Ergosterol Synthesis

Aspergillus fumigatus is a important opportunistic pathogen which can cause invasive aspergillosis that occurs mainly among immunocompromised and critically ill patlients. To date, three main classes of antifungal drugs that have different drug targets are used to treat severe human fungal infectins, namely azoles, polyenes and echinocandins. Azoles are the most widely used antifungal agents against Aspergillus fumigatus by inhibiting the activity of 14-a sterol demethylase (Cyp51/Erg11), a key enzyme that involved in ergosterol biosynthesis pathway. Ergosterol, the fungus-specific sterol and primarily distributed in plasma membranes,is essential for fungal membranes integrity and various biological functions including membrane fluidity,activity, signal transmission and so on. At the same time, ergosterol and its biosynthetic pathway also is a primary target for most antifungals that are currently used to treat fatal fungal infections. Further understanging the ergosterol biosynthesis pathway in Aspergillus fumigatus would be contribute to development of new antifungal agents.At present, the knowledge of the ergosterol biosynthesis process in the human fungal pathogen Aspergillus fumigatus remains limited. According to previous research findings that two homologous proteins coded by erg4A and erg4B which can catalyze the reaction during the final step of ergosterol biosynthesis were found in Aspergillus fumigatus. Single deletion of these erg4 revealed nothing alteration in canonical ergosterol biosynthesis while double deletions of erg4A and erg4B completely block the last step of ergosterol synthesis which resulting in a accumulation of ergosta-5,7,22,24(28)-tetraenol, a precursor compound of ergosterol And on this basis we have carried an in-depth study to determine the relationship between Erg4A and Erg4B. In this study, we found that ER-localized Erg4A and Erg4B all contain nine transmembrane structures. In addition, loss of one homolog of erg4 induces the overexpression of the other one, accompanied with the mRNA level of erg4B was higher than that of erg4A in the parental wild-type strain. These data verified that Erg4A and Erg4B have redundant functions during ergosterol biosynthesis and Erg4B may play a primary role in Aspergillus fumigatus.Further studies indicate that Erg4A and Erg4B are not required for hyphal growth but for conidiation which can be partly recovered by adding extra ergosteroL Importantly, the?erg4A?erg4B mutant strain exhibited hypersensitivity to antifungal azoles such as itraconazole and voriconazole, but still demonstrate wild-type virulence in a compromised mouse model. In conclusion, it will help to increase the antifungal effect of azole by inhibiting the expression of Erg4A and Erg4B.