title: The VirB5 protein localizes to the T-pilus tips in Agrobacterium tumefaciens.
abstract: The Agrobacterium tumefaciens VirB/D4 type IV secretion system (T4SS) mediates the transfer of single-stranded DNA and protein virulence factors into plant cells, and also determines the assembly of the T-pilus, which is believed to play a role in host recognition. The T-pilus is composed of the major component VirB2 and the minor component VirB5. Using immuno-electron microscopy we detected the major component VirB2 along the entire length of detached T-pili, but not on cell-bound T-pili or on the cell surface. In contrast, the minor T-pilus component VirB5 was detected on the tips of cell-bound T-pili as well as on the ends of detached T-pili and on the cell surface. To gain further insights into the role of VirB5 we introduced changes at its C terminus. C-terminal deletions of up to four amino acids and alanine replacements did not abolish T-pilus formation and incorporation of the VirB5 variants at the tip, although they did impact the length of T-pili. Also, these changes differentially affected the ability of the T4SS to transfer DNA into plant and bacterial recipients, suggesting differential effects on host-cell specificity. The data presented here suggest that VirB5 localizes at the T-pilus tip, and provide novel insights into its role during the type IV secretion process.
authors.affiliation: McMaster University, Department of Biology and Antimicrobial Research Centre, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada.
authors.forename: Khaled A
authors.initials: KA
authors.lastname: Aly
authors.affiliation: McMaster University, Department of Biology and Antimicrobial Research Centre, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada.
authors.forename: Christian
authors.initials: C
authors.lastname: Baron
mesh_terms: D016960:Agrobacterium tumefaciens / Q000378:metabolism / Q000472:pathogenicity*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000235:genetics / Q000378:metabolism; D010861:Fimbriae, Bacterial / Q000378:metabolism*; D017353:Gene Deletion; D031962:Kalanchoe / Q000382:microbiology; D016253:Microscopy, Immunoelectron; D010935:Plant Diseases / Q000382:microbiology; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004277:DNA, Single-Stranded