A Pyranose-2-Phosphate Motif Is Responsible for Both Antibiotic Import and Quorum-Sensing Regulation in Agrobacterium tumefaciens

Periplasmic binding proteins (pbps) in association with abc transporters select and import a wide variety of ligands into bacterial cytoplasm. they can also take up toxic molecules,as observed in the case of the phytopathogen agrobacterium tumefaciens strain c58. this organism contains a pbp called acca that mediates the import of the antibiotic agrocin 84,as well as the opine agrocinopine a that acts as both a nutrient and a signalling molecule for the dissemination of virulence genes through quorum-sensing. here,we characterized the binding mode of acca using purified agrocin 84 and synthetic agrocinopine a by x-ray crystallography at very high resolution and performed affinity measurements. structural and affinity analyses revealed that acca recognizes an uncommon and specific motif,a pyranose-2-phosphate moiety which is present in both imported molecules via the l-arabinopyranose moiety in agrocinopine a and the d-glucopyranose moiety in agrocin 84. we hypothesized that acca is a gateway allowing the import of any compound possessing a pyranose-2-phosphate motif at one end. this was structurally and functionally confirmed by experiments using four synthetic compounds: agrocinopine 3’-o-benzoate,l-arabinose-2-isopropylphosphate,l-arabinose-2-phosphate and d-glucose-2-phosphate. by combining affinity measurements and in vivo assays,we demonstrated that both l-arabinose-2-phosphate and d-glucose-2-phosphate,which are the accf mediated degradation products of agrocinopine a and agrocin 84 respectively,interact with the master transcriptional regulator accr and activate the quorum-sensing signal synthesis and ti plasmid transfer in a. tumefaciens c58. our findings shed light on the role of agrocinopine and antibiotic agrocin 84 on quorum-sensing regulation in a. tumefaciens and reveal how the pbp acca acts as vehicle for the importation of both molecules by means of a key-recognition motif. it also opens future possibilities for the rational design of antibiotic and anti-virulence compounds against a. tumefaciens or other pathogens possessing similar pbps. © 2015 el sahili et al.