Abstract
An Universal Stress Protein (USP) expressed under acid stress condition by Listeria innocua ATCC 33090 was investigated. The USP was up-regulated not only in the stationary phase but also during the exponential growth phase. The three dimensional (3D) structure of USP was predicted using a combined proteomic and bioinformatics approach. Phylogenetic analysis showed that the USP from Listeria detected in our study was distant from the USPs of other bacteria (such as Pseudomonas spp., Escherichia coli, Salmonella spp.) and clustered in a separate and heterogeneous class including several USPs from Listeria spp. and Lactobacillus spp. An important information on the studied USP was obtained from the 3D-structure established through the homology modeling procedure. In detail, the Model_USP-691 suggested that the investigated USP had a homo-tetrameric quaternary structure. Each monomer presented an architecture analogous to the Rossmann-like α/β-fold with five parallel β-strands, and four α-helices. The analysis of monomer-monomer interfaces and quality of the structure alignments confirmed the model reliability. In fact, the structurally and sequentially conserved hydrophobic residues of the β-strand 5 (in particular the residues V146 and V148) were involved in the inter-chains contact. Moreover, the highly conserved residues I139 and H141 in the region α4 were involved in the dimer association and functioned as hot spots into monomer–monomer interface assembly. The hypothetical assembly of dimers was also supported by the large interface area and by the negative value of solvation free energy gain upon interface interaction. Finally, the structurally conserved ATP-binding motif G-2X-G-9X-G(S/T-N) suggested for a putative role of ATP in stabilizing the tetrameric assembly of the USP. Therefore, the results obtained from a multiple approach, consisting in the application of kinetic, proteomic, phylogenetic and modeling analyses, suggest that Listeria USP could be considered a new type of ATP-binding USP involved in the response to acid stress condition during the exponential growth phase.
Highlights
Listeria innocua is regarded as a non-pathogenic indicator for the presence of Listeria monocytogenes in foods (Rosimin et al, 2016)
Acid stress response in L. monocytogenes has been the subject of several investigations, which documented the induction of a number of molecular mechanisms involving the F1F0-ATPase complex, the arginine deaminase (ADI) and the glutamate decarboxylase (GAD) pathways (Cotter et al, 2001; Ryan et al, 2009; Karatzas et al, 2012)
Little information is available on the role of Universal Stress Proteins (USPs) in the stress response of Listeria spp., the expression of USPs was already studied in numerous other microorganisms (Tkaczuk et al, 2013)
Summary
Listeria innocua is regarded as a non-pathogenic indicator for the presence of Listeria monocytogenes in foods (Rosimin et al, 2016). To L. innocua, pathogenic L. monocytogenes is frequently found in various foodstuffs (Kovacevic et al, 2012; Jami et al, 2014; Ebner et al, 2015; Melo et al, 2015), especially those characterized by pH values higher than 4.4 (CAC, 2009). Acid stress response in L. monocytogenes has been the subject of several investigations, which documented the induction of a number of molecular mechanisms involving the F1F0-ATPase complex, the arginine deaminase (ADI) and the glutamate decarboxylase (GAD) pathways (Cotter et al, 2001; Ryan et al, 2009; Karatzas et al, 2012). Little information is available on the role of Universal Stress Proteins (USPs) in the stress response of Listeria spp., the expression of USPs was already studied in numerous other microorganisms (Tkaczuk et al, 2013)
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