title: Functional divergence of FimX in PilZ binding and type IV pilus regulation.
abstract: Type IV pili (T4P) are polar surface structures that play important roles in bacterial motility, biofilm formation, and pathogenicity. The protein FimX and its orthologs are known to mediate T4P formation in the human pathogen Pseudomonas aeruginosa and some other bacterial species. It was reported recently that FimX(XAC2398) from Xanthomonas axonopodis pv. citri interacts with PilZ(XAC1133) directly through the nonenzymatic EAL domain of FimX(XAC2398). Here we present experimental data to reveal that the strong interaction between FimX(XAC2398) and PilZ(XAC1133) is not conserved in P. aeruginosa and likely other Pseudomonas species. In vitro and in vivo binding experiments showed that the interaction between FimX and PilZ in P. aeruginosa is below the measurable limit. Surface plasmon resonance assays further confirmed that the interaction between the P. aeruginosa proteins is at least more than 3 orders of magnitude weaker than that between the X. axonopodis pv. citri pair. The N-terminal lobe region of FimX(XAC2398) was identified as the binding surface for PilZ(XAC1133) by amide hydrogen-deuterium exchange and site-directed mutagenesis studies. Lack of several key residues in the N-terminal lobe region of the EAL domain of FimX is likely to account for the greatly reduced binding affinity between FimX and PilZ in P. aeruginosa. All together, the results suggest that the interaction between PilZ and FimX in Xanthomonas species is not conserved in P. aeruginosa due to the evolutionary divergence among the FimX orthologs. The precise roles of FimX and PilZ in bacterial motility and T4P biogenesis are likely to vary among bacterial species.
authors.affiliation: Division of Structural Biology & Biochemistry, School of Biological Sciences, Nanyang Technological University, Singapore.
authors.forename: Yaning
authors.initials: Y
authors.lastname: Qi
authors.forename: Linghui
authors.initials: L
authors.lastname: Xu
authors.forename: Xueming
authors.initials: X
authors.lastname: Dong
authors.forename: Yin Hoe
authors.initials: YH
authors.lastname: Yau
authors.forename: Chun Loong
authors.initials: CL
authors.lastname: Ho
authors.forename: Siew Lee
authors.initials: SL
authors.lastname: Koh
authors.forename: Susana Geifman
authors.initials: SG
authors.lastname: Shochat
authors.forename: Shan-Ho
authors.initials: SH
authors.lastname: Chou
authors.forename: Kai
authors.initials: K
authors.lastname: Tang
authors.forename: Zhao-Xun
authors.initials: ZX
authors.lastname: Liang
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D010861:Fimbriae, Bacterial / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D025941:Protein Interaction Mapping; D011550:Pseudomonas aeruginosa / Q000502:physiology*; D016415:Sequence Alignment; D020349:Surface Plasmon Resonance; D053532:Xanthomonas axonopodis / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D050505:Mutant Proteins; C097615:PilZ protein, Pseudomonas aeruginosa