Structural and functional characterization of Xanthomonas citri type IV secretion system.

Abstract

Bacteria uses different secretion systems for protein transportation to others bacteria, to eukaryotic cells or to be secreted in the extracellular medium. Among them, type IV secretion system, T4SS, is perhaps the most versatile, being present in both Gram-positive and Gram-negative bacteria; it is also capable to transport protein-DNA complexes, mediating horizontal gene transfer, an important mechanism for molecular evolution. T4SS is an important virulence mechanism being used by some bacteria to release toxins into the host cell, such as Agrobacterium tumefaciens, Legionella pneumophila, Helicobacter pylori and Brucella suis. Curiously, in recent years, it has been identified that Xanthomonas citri (and some other species of Xanthomonadaceae family) possess an atypical T4SS capable to kill other bacterial species through toxin secretion. Xanthomonas citri has high economical interest, due to be responsible for citrus canker, a disease affecting citrus caused by this bacteria resulting in lesions on the leaves and fruits losses. The project here proposed has the goal to express, to purificate and to obtain structural insights about the whole Xanthomonas T4SS system. This project main challenge is due the size of this complex (higher than 3MDa) and the fact that it is associated with both inner and external membranes. In parallel, two individual components will be studied - VirB1 (a periplasmatic transglucosidase) and VirB2 (a subunit of this system extracellular pilus). We expect that the knowledge obtained during this project development will provide us a better understanding of T4SS mechanism related to alternatives secretion functions. These studies will also serve as base for the development of new drugs and in the bioremediation practice.