Proteome Profile of Aspergillus terreus Conidia at Germinating Stage: Identification of Probable Virulent Factors and Enzymes from Mycotoxin Pathways

Abstract

Aspergillus terreus is an emerging opportunistic fungal pathogen that causes invasive aspergillosis in immunocompromised individuals. The main risk group of individuals for this organism is leukopenic patients, individuals having cancers, bone marrow transplant persons and those who have immunological disorders. The lack of early diagnostic marker for A. terreus and intrinsic resistance to Amphotericin B, further limits the successful therapy of A. terreus-associated infections. The germination of inhaled conidia is the key step to establish successful invasion in host tissues or organs. Thus, profiling of expressed proteins during germination of conidia not only shed light on proteins that are involved in invasion or virulence but may also provide early diagnostic markers. We used nanoLC-Q-TOF to study the proteome of germinating conidia (at 16 h time points) of A. terreus. We observed expression of 373 proteins in germinating conidia of A. terreus. A total of 74 proteins were uncharacterized in the database. The expressed proteins were associated with various processes like cell wall modulation, virulence factors and secondary metabolite biosynthesis. The most abundant proteins were associated with protein biosynthesis, carbohydrate metabolism and unknown functions. Among virulent proteins, mitogen-activated protein kinase (hog1) and mitogen-activated protein kinase (mpkC) are key virulent proteins observed in our study. We observed 7 enzymes from terretonin and 10 enzymes from geodin mycotoxin biosynthesis pathway. Interestingly, we observed expression of terrelysin protein, associated with blood cell lysis. Quantitative RT-PCR analysis showed 26-fold increase in transcripts encoding for dihydrogeodin oxidase and 885-fold for terrelysin gene in germinating conidia in comparison to conidia. Further, we propose that terrelysin protein and secondary metabolite such as geodin could be explored as diagnostic marker for A. terreus-associated infections.

Invasive <em>Aspergillus terreus</em> morphological transitions and immunoadaptations mediating antifungal resistance

“… 19 , 22 Important factors affecting A. terreus virulence are inoculum size, host characteristics, 24 and the expression of terrelysin (a hemolytic protein), CgrA, CREB, PepP, MyoA, Mep, Hog1, and MPKC, secreted during germination of A. terreus conidia. 13 Remarkably, the rate of A. terreus infection increases proportionally with the pathogen inoculum, but inoculum size does not affect intrinsic host characteristics. 24 , 25 Therefore, it is important to understand key morphological aspects of PC and AC, and how they influence host colonization.…”

“… 10 – 12 Given successful germination of A. terreus conidia is the key step to invasive aspergillosis, a recent proteomic study uncovered virulent proteins, such as Hog1 and MPKC, and high-level transcripts, such as the DHO and TER genes, associated with the transition stages that are a hallmark of conidia germination. 13 …”

Resistance mechanism and proteins in Aspergillus species against antifungal agents

“…at development stages (Asif et al 2006 ; Suh et al 2012 ; Tiwari et al 2016 ; Thakur and Shankar 2017 ). Comparative proteome analysis of resting conidia to mycelia provided biochemical and cellular pathway during the morphotypes of Aspergilli (Asif et al 2006 ; Vodisch et al 2009 ; Teutschbein et al 2010 ; Tiwari et al 2016 ; Thakur and Shankar 2017 ; Shankar et al 2018 ). To date, proteomic-based analysis on how Aspergilli adapt to host condition has conceded information of Aspergilli infection mechanisms (Suh et al 2012 ; Kubitschek-Barreira et al 2013 ).…”

Molecular Insights Into Development and Virulence Determinants of Aspergilli: A Proteomic Perspective

“…But this technique has some limitations such as in the detection of low abundant proteins or resolution of large number of proteins. In last few years the shot gun approach has gained importance to carry out proteome analysis of Aspergilli at different conditions such as during morphological transitions to stress conditions (in exposure to antifungal or different carbon sources; Suh et al, 2012 ; Novodvorska et al, 2016 ; Tiwari et al, 2016 ; Thakur and Shankar, 2017a ). Such studies revealed the broad biological nature of these Aspergilli as well as their survival needed in the environment where they face multi-factorial challenges.…”

“…Recently, Thakur and Shankar reported proteins from germinating conidia or conidial proteins of A. terreus . A total of 42 conidial proteins were observed and majority of these proteins were from secondary metabolite biosynthesis, lipid metabolism and protein biosynthesis (Thakur and Shankar, 2017a ). Recently transcriptomic/translational study by Novodvorska et al demonstrated that A. niger conidia suspended in water have metabolic activity as compared to completely dried conidia.…”