The crystal structure of two macrolide glycosyltransferases provides a blueprint for host cell antibiotic immunity

Abstract

Glycosylation of macrolide antibiotics confers host cell immunity from endogenous and exogenous agents. The Streptomyces antibioticus glycosyltransferases, OleI and OleD, glycosylate and inactivate oleandomycin and diverse macrolides including erythromycin, respectively. The structure of these enzyme-ligand complexes, in tandem with kinetic analysis of site-directed variants, provide insight into the interaction of macrolides with their synthetic apparatus. Erythromycin binds to OleD and the 23S RNA of its target ribosome in the same conformation and, although the antibiotic contains a large number of polar groups, its interaction with these macromolecules is primarily through hydrophobic contacts. Erythromycin and oleandomycin, when bound to OleD and OleI, respectively, adopt different conformations, reflecting a subtle effect on sugar positioning by virtue of a single change in the macrolide backbone. The data reported here provide structural insight into the mechanism of resistance to both endogenous and exogenous antibiotics, and will provide a platform for the future redesign of these catalysts for antibiotic remodelling.

Fig. 1.

The mechanism of macrolide antibiotic resistance in S. antibioticus.

Fig. 2.

The reactions catalyzed by OleI and OleD. The enzymes transfer glucose from UDP-glucose to the O2 position of the desosamine sugar appended to the macrolide backbone of macrolide antibiotics. The reaction occurs with inversion of anomeric configuration to generate the β-glucoside.

Fig. 3.

The three-dimensional structures of OleI (A) and OleD (B) shown as divergent (“wall-eyed”) stereo cartoons. It can be seen that the domains of OleD lie in a more open conformation than those of OleI.

Fig. 4.

Observed electron density for ligands bound to OleI. A divergent stereo (divergent) view of the observed electron density (maximum-likelihood weighted 2F_obs − F_calc contoured at 1 σ/0.5 electrons/A³) of the complex of OleI with UDP (blue electron density) and oleandomycin (red electron density) with interacting residues shown in ball-and-stick.