Identification of the efectors of Rickettsia rickettsii type four secretion system

• Grant number: 14/06032-4
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: July 01, 2014
• End date: December 31, 2016
• Field of knowledge: Biological Sciences - Genetics - Molecular Genetics and Genetics of Microorganisms
• Principal Investigator: Andréa Cristina Fogaça
• Grantee: Maria Fernanda Bandeira de Melo Galletti
• Host Institution: Instituto de Ciências Biomédicas (ICB). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 13/26450-2 - Molecular characterization of the interactions among ticks, rickettsiae and vertebrate hosts, AP.TEM

Abstract

Rickettsia rickettsii is the etiological agent that causes Rocky Mountain spotted fever, which is the most lethal spotted fever rickettsiosis that affects humans. R. rickettsii is an obligate intracellular alpha-proteobacteria, aerobic, which survive within cytoplasm and/or nucleus of the host cell. The main tick species that transmits R. rickettsii in São Paulo's metropolitan area is Amblyomma aureolatum. Pioneer studies demonstrated that R. rickettsii require higher temperatures and the vector's blood meal to reactivate its virulence. Nevertheless, the molecular mechanisms responsible for this phenotype conversion have not been completely elucidated. Our research group determined the effects of these environmetal stimuli on the global gene expression profile of this bacterium. We observed that virulence factors, including some components of type four secretion system (T4SS), are induced by blood-feeding. The T4SS is a protein complex that allows the delivery of molecules, known as effectors, to the host cell. Within the cytoplasm, those effectors play different roles on cell essential activities such as bacterial replication and evasion of host immune system. However, there are no studied that characterize the function of R. rickettsii effector proteins. In this manner, the present study aims to identify the effector proteins of the T4SS of R. rickettsii. We initially will perform in silico analysis (hydropathy score analysis, eukaryotic conserved domains and absence of signal peptide) to predict candidate proteins to effectors. Following in silico selection, proteins that interact with the T4SS recruiter protein, VirD4, will be identified using a two-hybrid system. Subsequently, we will evaluate the translocation of those proteins by T4SS using the model secretion system of Legionella pneumophila. At last, we will assess the effect of antibodies anti-effector on R. rickettsii in vitro. This study will indicate factors directly involved on rickettsial virulence, which might be considered as targets for vaccines in the future.