How Macrolide Antibiotics Work

Macrolide antibiotics inhibit protein synthesis by targeting the bacterial ribosome. They bind at the nascent peptide exit tunnel and partially occlude it. Thus, macrolides have been viewed as ‘tunnel plugs’ that stop the synthesis of every protein. More recent evidence, however, demonstrates that macrolides selectively inhibit the translation of a subset of cellular proteins, and that their action crucially depends on the nascent protein sequence and on the antibiotic structure. Therefore, macrolides emerge as modulators of translation rather than as global inhibitors of protein synthesis. The context-specific action of macrolides is the basis for regulating the expression of resistance genes. Understanding the details of the mechanism of macrolide action may inform rational design of new drugs and unveil important principles of translation regulation. Ribosome-targeting macrolide antibiotics were thought to simply plug the nascent peptide exit tunnel and interrupt the synthesis of any protein. However, structural, biochemical, and genome-wide studies have revealed that macrolides are highly selective modulators of protein synthesis. Macrolide molecules together with specific nascent peptides in the ribosomal tunnel allosterically affect the functional properties of the catalytic center of the ribosome. The macrolide-bound ribosome is unable to polymerize specific amino acid sequences in the nascent protein. Programmed translation arrest that controls the expression of macrolide resistance genes exploits the context-specific action of macrolides. The principles of the interplay between macrolides and nascent peptides that modulate the functions of the ribosome may apply to translational control exerted by other small molecules that interact with the ribosome.