Identification and characterization of agrobacterium tumefaciens virD2-binding protein

Abstract

In this thesis, a novel A. tumefaciens VirD2-binding protein (VBP) was identified. Homologous search showed that A. tumefaciens has two additional genes highly homologous to the identified vbp gene. So, A. tumefaciens contains the redundancy of three homologs for the VirD2-binding protein. Mutations of three vbp genes showed that VBP proteins were involved in the tumorigenesis of A. tumefaciens. Pull-down and co-immunoprecipitation results showed that VBP proteins could bind both VirD2 and some components of VirB/D4 type IV secretion system (T4SS). The C-terminal sequence of VBP proteins possess an important feature of the known T4SS substrates, indicating that VBP proteins may help T-complex to be recruited to VirB/D4 transport apparatus. VBP proteins were also shown to be involved in some plasmid conjugation system. Therefore, VBP proteins were defined as a new class of proteins; recruiting proteins that can recruit the cytoplasmic DNA transfer intermediate to the membrane transport apparatus.