Substituents at N6 and C‐5′ Control Selective Uptake and Toxicity of the Adenine‐Nucleotide Bacteriocin, Agrocin 84, in Agrobacteria

Abstract

The inhibition of a sensitive strain of Agrobacterium radiobacter by the nucleotide bacteriocin agrocin 84 has been studied. A structure‐function study of the agrocin 84 molecule was undertaken. Two agrocin 84 nucleotide fragments lacking either the N6 or 5′‐phosphoramidate substituents were used in uptake studies of [32P2]agrocin 84. It was established that the plasmid‐controlled, strain‐specific uptake of agrocin 84 is determined by the N6‐d‐glucofuranosyloxyphosphoramidate substituent. This conclusion is further supported by the markedly reduced uptake of the 32P‐labelled fragment lacking the N6 substituent. Equilibrium dialysis studies also indicate that the N6 substituent is ‘recognised’ by a binding protein involved in the uptake of agrocin 84 into sensitive strains. The nucleotide fragment bearing the N6 substituent is a competitive inhibitor for the uptake of agrocin 84 in vivo with a Ki−1.0 × 10−7 M and is itself selectively transported into a sensitive strain at a rate comparable with agrocin 84, but unlike agrocin 84 is non‐toxic. By contrast, the fragment bearing the 5′‐phosphoramidate is taken up by both sensitive and insensitive strains at a barely measurable rate and is toxic to both. Copyright © 1981, Wiley Blackwell. All rights reserved