The ribonucleolytic activity of the ribotoxin α-sarcin is not essential for in vitro protein biosynthesis inhibition

Fungal ribotoxins are toxic secreted ribonucleases that cleave a conserved single phosphodiester bond located at the sarcin/ricin loop of the larger rRNA. This cleavage inactivates ribosomes leading to protein biosynthesis inhibition and cell death. It has been proposed that interactions other than those found at the active site of ribotoxins are needed to explain their exquisite specific activity. The study presented shows the ability of a catalytically inactive α-sarcin mutant (H137Q) to bind eukaryotic ribosomes and interfere with in vitro protein biosynthesis. The results obtained are compatible with previous observations that α-sarcin can promote cell death by a mechanism that is independent of rRNA cleavage, expanding the potential set of activities performed by this family of toxins.

► Ribotoxins inactivate ribosomes by cleaving a conserved single phosphodiester bond.
► Ribosome inactivation leads to protein biosynthesis inhibition and cell death.
► Catalytically inactive α-sarcin mutant H137Q inhibits in vitro protein synthesis.
► Wild-type and H137Q α-sarcin bind to and cosediment with ribosomes.
► Ribotoxins’ binding to ribosomes seems to suffice for impairing protein synthesis.