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Infect. Immun. doi:10.1128/IAI.00484-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Total, membrane, and immunogenic proteomes of macrophage- and tick cell-derived Ehrlichia chaffeensis evaluated by LC-MS/MS and MALDI-TOF methods

Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Department of Biochemistry, College of Arts and Sciences, Kansas State University, Manhattan, KS 66506

^* To whom correspondence should be addressed. Email: rganta{at}vet.ksu.edu.

	Abstract

Ehrlichia chaffeensis, a tick-transmitted rickettsial, is the causative agent of human monocytic ehrlichiosis. To examine protein expression patterns, we analyzed total, membrane and immunogenic proteomes of E. chaffeensis originating from macrophage and tick cell cultures. Total proteins resolved by one-dimensional gel electrophoresis and subjected to GeLC-MS/MS allowed identification of 134 and 116 proteins from macrophage- and tick cell-derived E. chaffeensis, respectively. Because a majority of immunogenic proteins remained in the membrane fraction, individually picked total and immunogenic membrane proteins were also surveyed by LC-MS/MS and MALDI-TOF methods. The analysis aided the identification of 48 additional proteins. In total, 278 genes of the E. chaffeensis genome were verified as functional genes. They included genes for DNA and protein metabolism, energy metabolism and transport, membrane proteins, hypothetical proteins and many novel proteins of unknown function. The data reported in this study suggest that the membrane of E. chaffeensis is very complex, having many expressed proteins. This study represents the first and the most comprehensive analysis of E. chaffeensis expressed proteins. This also is the first study confirming expression of nearly one-fourth of all predicted genes of the E. chaffeensis genome, validating that they are functionally active genes, and demonstrates that classic shotgun proteomic approaches are feasible for tick-transmitted intra-phagosomal bacteria. The identity of novel expressed proteins reported in this study, including the large selection of membrane and immunogenic proteins, will be valuable in elucidating pathogenic mechanisms and developing effective prevention and control methods.