Structural insights on hypothetical proteins, secretion chaperones from Xanthomonas axonopodis pv. citri

Author(s)

Juliana Fattori

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2011-09-16

Examining board members

Ljubica Tasic; Mário Tyago Murakami; Letícia Khater; Wanda Pereira Almeida; Anita Jocelyne Marsaioli

• Advisor: Ljubica Tasic

Abstract

The aim of this study was the structural characterization of four possible secretion chaperones from the bacterium Xanthomonas axonopodis pv. citri (Xac). This characterization is very important to better understand the function of such proteins and the virulence mechanisms from Xac, which is the bacterium responsible for provoking the citrus canker. Among the target proteins, XACb0033 is a possible secretion chaperone from type IV secretion system, XAC0419 and XAC1346 are possible secretion chaperones from type III secretion system and XAC1990 was earlier identified as a flagellar protein (FlgN). All four target proteins, cloned into pET23a, were expressed in E. coli, purified and found folded as observed in the circular dichroism analyses (CD). It was also verified (CD experiments) that these proteins have a high helical content. These proteins were further characterized by analytical gel filtration, mass spectrometry (MS), diffusion techniques in nuclear magnetic resonance (DOSY-NMR) and small angle X-ray scattering (SAXS). Molecular envelops were built for two target proteins applying the SAXS data. These envelops were in good agreement with the 3D structures predicted by bioinformatics. Finally, XAC0419 was considered a possible class I secretion chaperone based on the obteined results. XAC1990 (FlgN) was confirmed as a flagellar chaperone (class III), while obtained results for XACb0033 pointed structural similarity with VirE1, the unique type IV secretion system chaperone known so far (AU)