Regulation of Xanthomonas citri Type IV pilus

• Grant number: 15/17073-6
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: September 01, 2015
• End date: January 31, 2016
• Field of knowledge: Biological Sciences - Biochemistry - Chemistry of Macromolecules
• Principal Investigator: Shaker Chuck Farah
• Grantee: Raphael Dias Teixeira
• Host Institution: Instituto de Química (IQ). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 11/07777-5 - Cyclic di-GMP signaling and the Type IV macromolecule secretion system in Xanthomonas citri, AP.TEM

Abstract

Type IV pili (T4P) are bacterial surface structures that partake in different bacterial behaviours including twitching motility, surface adhesion, natural transformation, biofilm formation protein secretion and chemotaxis. The T4P filament is a flexible helicoidal 60-80 Å polymer made up mostly of PilA subunits that are processed by the prepilin peptidase PilD before being incorporated into the T4P base at the bacterial inner membrane. These mature pilins are polymerized by PilB and depolymerized by PilT, both hexameric ATPases (see Figure 5 of the Thematic Project). T4P formation (biogenesis) and regulation is a complex and little understood process involving a large number of proteins (40 described in Pseudomonas). T4P are required for bacterial twitching, a coordinated movement of small groups of cells over a solid surface. Cell are able to move over surfaces by means of cycles of T4P extension (polymerization), adhesion and retraction (depolymerization). Biogenesis, polymerization and depolymerization of T4P are controlled by environmental factors ina a manner that is not well understood but that depends, at least in part, on the FimX protein that contains RR-PAS-GGDEF-EAL domains, as well as the PilZ protein. Interestingly, structural and enzymatic studies showed that the GGDEF and EAL domains of FimX are inactive. However, the EAL domain has retained the ability to bind c-di-GMP and this binding controls its polar localization (in Pseudomonas). The Xac genome codes for all the proteins required for the formation of a functional T4P and our group has been studying this system over the past several years. We resolved the structure of PilZXAC1133 and showed that it does not bind c-di-GMP but interacts with the FimXXAC2398 EAL domain ad with the PilBXAC3239 ATPase. However, the role of the T4P in Xac motility and other behaviors and the means by which FimX and PilZ contribute to the regulation of T4P biogenesis in response to c-di-GMP, possibly via its interactions with PilB, are unknown.