Abstract
Agrobacterium pathogens of octopine- and nopaline-types force host plants to produce either octopine or nopaline compounds, which they use as nutrients. Two Agrobacterium ABC-transporters and their cognate periplasmic binding proteins (PBPs) OccJ and NocT import octopine and nopaline/octopine, respectively. Here, we show that both octopine transport and degradation confer a selective advantage to octopine-type A. tumefaciens when it colonizes plants. We report the X-ray structures of the unliganded PBP OccJ and its complex with octopine as well as a structural comparison with NocT and the related PBP LAO from Salmonella enterica, which binds amino acids (lysine, arginine and ornithine). We investigated the specificity of OccJ, NocT and LAO using several ligands such as amino acids, octopine, nopaline and octopine analogues. OccJ displays a high selectivity and nanomolar range affinity for octopine. Altogether, the structural and affinity data allowed to define an octopine binding signature in PBPs and to construct a OccJ mutant impaired in octopine binding, a selective octopine-binding NocT and a non-selective octopine-binding LAO by changing one single residue in these PBPs. We proposed the PBP OccJ as a major trait in the ecological specialization of octopine-type Agrobacterium pathogens when they colonize and exploit the plant host.
Highlights
Opines are low molecular weight (200 to 600 g/mol) carbon compounds, characteristic of crown-gall tumors induced by pathogenic, soil-inhabiting Agrobacterium species
This very efficient binding ability may have contributed to the specialization of the octopine-type A. tumefaciens, and explains why the nopaline-type agrobacteria which display a drastically lower affinity for both nopaline and octopine do not spread despite the advantage associated with broader nutritional niches
This work mainly focused on the study of the specificity of three related periplasmic binding proteins (PBPs): OccJ and NocT, both encoded by the Ti-plasmid of octopine and nopaline-type Agrobacterium strains, respectively, and S. enterica LAO for Lysine-Arginine-Ornithine, belonging to the same PBP structural cluster
Summary
Opines are low molecular weight (200 to 600 g/mol) carbon compounds, characteristic of crown-gall tumors induced by pathogenic, soil-inhabiting Agrobacterium species. The mutation of a single amino acid in NocT and LAO can modify their ligand selectivity to transform them into octopine selective and non-selective PBPs, respectively, our work shows that OccJ is evolved for binding octopine and octopinic acid with high affinity in nanomolar range mainly due to the presence of a serine at position 91. This very efficient binding ability may have contributed to the specialization of the octopine-type A. tumefaciens, and explains why the nopaline-type agrobacteria (generalists) which display a drastically lower affinity (micromolar range) for both nopaline and octopine do not spread despite the advantage associated with broader nutritional niches
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
