Salmonella Typhimurium's Transthyretin-Like Protein Is a Host-Specific Factor Important in Fecal Survival in Chickens

Abstract

The transthyretin-like protein (TLP) from Salmonella enterica subspecies I is a periplasmic protein with high level structural similarity to a protein found in mammals and fish. In humans, the protein homologue, transthyretin, binds and carries retinol and thyroxine, and a series of other, unrelated aromatic compounds. Here we show that the amino acid sequence of the TLP from different species, subspecies and serovars of the Salmonella genus is highly conserved and demonstrate that the TLP gene is constitutively expressed in S. Typhimurium and that copper and other divalent metal ions severely inhibit enzyme activity of the TLP, a cyclic amidohydrolase that hydrolyses 5-hydroxyisourate (5-HIU). In order to determine the in vivo role of the S. Typhimurium TLP, we constructed a strain of mouse-virulent S. Typhimurium SL1344 bearing a mutation in the TLP gene (SL1344 ΔyedX). We assessed the virulence of this strain via oral inoculation of mice and chickens. Whilst SL1344 ΔyedX induced a systemic infection in both organisms, the bacterial load detected in the faeces of infected chickens was significantly reduced when compared to the load of S. Typhimurium SL1344. These data demonstrate that the TLP gene is required for survival of S. Typhimurium in a high uric acid environment such as chicken faeces, and that metabolic traits of Salmonellae in natural and contrived hosts may be fundamentally different. Our data also highlight the importance of using appropriate animal models for the study of bacterial pathogenesis especially where host-specific virulence factors or traits are the subject of the study.

Cooperative regulation of the common target genes between H2O2-sensing YedVW and Cu2+-sensing CusSR in Escherichia coli

“…One possible role of HiuH is to rapidly reduce possible oxidative damage which might occur if 5-HIU was allowed to spontaneously decompose under normal conditions (Hennebry et al, 2012). When Cu 2+ ions were present at an equimolar concentration to 5-HIU, the activity of HiuH was strongly inhibited in Salmonella (Hennebry et al, 2012). These results suggested that Cu 2+ -dependent regulation of uric acid metabolism is important for resistance to oxidative stress in E. coli.…”

“…In E. coli, unused purines are degraded to uric acid (Vogels & Van der Drift, 1976;Xi et al, 2000), which is then degraded to allantoin via 5-HIU and 2-oxo-hydroxy-4-caroxy-5-ureidoimadeazline (OHCU) (Lee et al, 2005;Hennebry et al, 2012). Under anaerobic conditions, allantoin is further degraded to provide nitrogen sources, whilst under aerobic conditions it is degraded to 3-phosphoglycerate via glyoxylate for energy production.…”

“…The non-enzymic pathway is known as the intermediate pathway for the conversion of uric acid to allantoin, but the enzymes involved in these reaction steps remain unidentified (Xi et al, 2000). Recently, however, the enzyme for the conversion of 5-HIU to OHCU was identified as the hiuH (yedX) gene product (Lee et al, 2005;Hennebry et al, 2012). Urate is generally considered as an antioxidant, but under some circumstances it enhances oxidative stress because urate switches between being a prooxidant or antioxidant depending on the Cu 2+ concentration (Filipe et al, 2002).…”

“…Association of the enzymic machinery of the purine metabolism pathway has not been established in the periplasm (Hennebry et al, 2012). One possible role of HiuH is to rapidly reduce possible oxidative damage which might occur if 5-HIU was allowed to spontaneously decompose under normal conditions (Hennebry et al, 2012).…”

“…As a result, at least three YedW-binding sites were identified within the intergenic spacer regions cyoA,,ampG, yedW,.hiuH and cusR,.cusC (where the arrowheads indicate the direction of transcription). The gene product HiuH is a transthyretin-like protein and in Salmonella it functions as the hydrolase of 5-hydroxyisourate (5-HIU), a degradation product of uric acid, in the purine catabolism pathway (Lee et al, 2005;Hennebry et al, 2012). The possible influence in vivo of YedW on the predicted promoters for the target gene promoters was analysed using the LacZ reporter assay.…”