Global Proteomic Analysis of Human Ehrlichiosis Agents
EMSL Project ID
25412
Abstract
Obligatory intracellular bacteria (belonging to Rickettsia): Ehrlichia chaffeensis and Anaplasma phagocytophilum cause potentially fatal emerging zoonoses: human monocytic ehrlichiosis and human granulocytic anaplasmosis, respectively. The severity of disease varies from subclinical infection to severe morbidity that requires hospitalization, or death. These pathogens are most commonly found in the environment. Similar to Rickettsia rickettsii, which causes Rocky Mountain spotted fever, wild animals such as deer and rodents are natural reservoirs of these pathogens. Bacteria are transmitted to humans from wild animal reservoirs by the bite of infected ticks, thus environmental changes and human outdoor activities affect disease distribution and prevalence. No vaccines are currently available and only one broad spectrum antibiotic, doxycycline, is effective for treatment of human ehrlichioses. Obligatory intracellular bacteria hijack host cell physiology and membrane biogenesis. Despite the progress made in deciphering the complete nucleotide sequences of the genomes of A. phagocytophilum and E. chaffeensis (PLoS Genetics 2006, 2: e21 1-16), how these bacteria survive and persist in the hosts are unexplained. Research on obligatory intracellular bacteria requires innovative systematic approaches, since the dynamic interactions between the ensemble of bacterial and host cell proteins involve in survival and persistence of these bacteria in the reservoir, vector, and accidental human hosts.
In Aim 1, we propose to analyze the global proteomes of E. chaffeensis and A. phagocytophilum, which mutually exclusively infect monocytes and granulocytes, respectively. The two bacteria share approximately 75% gene sequence identity, with the remaining genes unique to each. Global analysis of the membrane and cytosolic proteins in these bacteria would help delineate host cell tropism, membrane signaling, and persistence. The study will synergize with one of our current research aims to understand the signaling mechanism by which these bacteria replicate inside hostile leukocytes, which are primary host defensive cells (funded by NIH, grant No. R01AI30010). In Aim 2, we propose to determine global proteomes of these bacteria in human leukocytes and tick cells. Distinct sets of proteins produced during two essential stages of bacteria: mammalian and tick stages would hold a key for understanding tick transmission of these bacteria between mammals. Aim 2 is distinct from Aim 1 with respect to specimens. In Aim 2, we will analyze whole infected cells. There are several rationales for this approach. First, these intracellular bacteria secrete some proteins directly into the cytoplasm of the host cells via the type IV secretion mechanism to modulate host cell functions (funded by NIH, grant No. R01AI54476). Thus, whole infected cells should contain these secreted proteins important for interaction with host cells. Second, membrane protein analysis provides information on bacterial proteins bound to host membranes. Third, whole infected cells provide membrane and soluble protein proteomes of human and tick host cells altered in response to intracellular bacterial infection. For example, activated signaling proteins often translocate from the cytosol to the membrane. The results of this study will promote understanding of the complex interplay between membrane and soluble proteins in establishing obligatory intracellular parasitism.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2007-06-06
End Date
2010-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Brewer HM, AD Norbeck, JN Adkins, NP Manes, C Ansong, L Shi, Y Rikihisa, T Kikuchi, S Wong, RD Estep, F Heffron, L Pasa-Tolic, and RD Smith. 2008. "Optimization of proteomic sample preparation procedures for comprehensive protein characterization of pathogenic systems." Journal of Biomolecular Techniques:JBT 19(5):285-295.
Huang H, M. Lin, X Wang, T Kikuchi, HM Mottaz, AD Norbeck, and Y Rikihisa. 2008. "Proteomic Analysis of and Immune Responses to Ehrlichia chaffeensis Lipoproteins." Infection and Immunity 76(8):3405-3414. doi:10.1128/IAI.00056-08.