Comparative proteomic analysis of the PhoP regulon in Salmonella enterica serovar Typhi versus Typhimurium.
BACKGROUND
S. Typhi, a human-restricted Salmonella enterica serovar, causes a systemic intracellular infection in humans (typhoid fever). In comparison, S. Typhimurium causes gastroenteritis in humans, but causes a systemic typhoidal illness in mice. The PhoP regulon is a well studied two component (PhoP/Q) coordinately regulated network of genes whose expression is required for intracellular survival of S. enterica.


RESULTS
Using high performance liquid chromatography mass spectrometry (HPLC-MS/MS), we examined the protein expression profiles of three sequenced S. enterica strains: S. Typhimurium LT2, S. Typhi CT18, and S. Typhi Ty2 in PhoP-inducing and non-inducing conditions in vitro and compared these results to profiles of phoP(-)/Q(-) mutants derived from S. Typhimurium LT2 and S. Typhi Ty2. Our analysis identified 53 proteins in S. Typhimurium LT2 and 56 proteins in S. Typhi that were regulated in a PhoP-dependent manner. As expected, many proteins identified in S. Typhi demonstrated concordant differential expression with a homologous protein in S. Typhimurium. However, three proteins (HlyE, STY1499, and CdtB) had no homolog in S. Typhimurium. HlyE is a pore-forming toxin. STY1499 encodes a stably expressed protein of unknown function transcribed in the same operon as HlyE. CdtB is a cytolethal distending toxin associated with DNA damage, cell cycle arrest, and cellular distension. Gene expression studies confirmed up-regulation of mRNA of HlyE, STY1499, and CdtB in S. Typhi in PhoP-inducing conditions.


CONCLUSIONS
This study is the first protein expression study of the PhoP virulence associated regulon using strains of Salmonella mutant in PhoP, has identified three Typhi-unique proteins (CdtB, HlyE and STY1499) that are not present in the genome of the wide host-range Typhimurium, and includes the first protein expression profiling of a live attenuated bacterial vaccine studied in humans (Ty800).
Charles
Richelle C
RC
Division of Infectious Diseases, Massachusetts General Hospital, Boston, Massachusetts, USA. rccharles@partners.org
Harris
Jason B
JB
Chase
Michael R
MR
Lebrun
Lauren M
LM
Sheikh
Alaullah
A
LaRocque
Regina C
RC
Logvinenko
Tanya
T
Rollins
Sean M
SM
Tarique
Abdullah
A
Hohmann
Elizabeth L
EL
Rosenberg
Ian
I
Krastins
Bryan
B
Sarracino
David A
DA
Qadri
Firdausi
F
Calderwood
Stephen B
SB
Ryan
Edward T
ET
D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism*; D001428:Bacterial Vaccines / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D051379:Mice; D008954:Models, Biological; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D040901:Proteomics / Q000379:methods*; D012485:Salmonella typhi / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000378:metabolism*; D013045:Species Specificity; D014774:Virulence / Q000235:genetics
D001426:Bacterial Proteins; D001428:Bacterial Vaccines; D010455:Peptides; C061064:PhoP protein, Bacteria