Abstract
The most prevalent airborne human pathogenic fungus Aspergillus fumigatus is ubiquitous in soil and like other ascomycotous fungi it can utilize a variety of nitrogen sources. Nitrogen metabolite repression (NMR) may induce virulence in A. fumigatus as in pathogenic fungi but the mechanism of regulation and its key components are not identified. The present study focuses on the molecular modeling and in silico characterization of the main player of this regulation, the NmrA of A. fumigatus. Physiochemical and structural characterization using various sequence and structure based predictors and quality assessment of the proposed two- and three-dimensional models were carried out. The characteristic motifs such as glycine-rich NAD(P)-binding motif (GxxGxxG) and altered active site motif (HxxxK) were located in NmrA along with DNA-binding residues (T11, R39, D40 and A45). The results obtained using bioinformatics tools indicated that the protein was hydrophilic in nature, stable in vitro and had very low disorder probability. Based on the quality score, the proposed secondary and tertiary structures were correct and extremely good to represent NmrA of A. fumigatus. Phylogenetic analysis signified its close relation with NMR regulatory protein of opportunistic human pathogens A. lentulus and A. novofumigatus.
Highlights
The opportunistic human pathogen, Aspergillus fumigatus is a ubiquitous saprophytic fungus, which is associated with various diseases of the respiratory tract
In the most prevalent airborne pathogenic fungus A. fumigatus, NmrA is repressor of the GATA transcriptional factor AreA, which regulates several genes required for utilization of less-preferred nitrogen sources such as nitrate (Tudzynski, 2014)
The bZIP protein MeaB is an activator of NmrA (Wong et al, 2007). These three regulatory proteins NmrA, AreA and MeaB are highly conserved in filamentous fungi (Wagner et al, 2010)
Summary
The opportunistic human pathogen, Aspergillus fumigatus is a ubiquitous saprophytic fungus, which is associated with various diseases of the respiratory tract. NMR is a global regulatory switch which controls activation of enzyme and permease coding genes for degradation of non-preferred nitrogen sources (Magasanik and Kaiser, 2002). The major GATA transcription factor AreA and its co-repressor NmrA play a vital role in nitrogen regulatory network (Tudzynski, 2014). Inactivation of these regulatory proteins results in inability of fungal growth on nitrogen sources except for ammonium and glutamine (Wilson and Arst, 1998). NmrA is among the highly conserved regulatory proteins among Aspergillus species (Lamb et al, 2003). NmrA is a member of the short-chain dehydrogenase reductase (SDR)
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