The cytotoxic A1 domain of shiga‐like toxin 1 interacts with two distinct sites on the ribosomal stalk

Abstract

Ribosome‐inactivating proteins (RIPs) such as Shiga‐like toxin 1 (SLT‐1) halt protein synthesis in eukaryotic cells by depurinating a single adenine base in the sarcin‐ricin loop of 28S rRNA. The molecular details leading up to the site‐specific depurination are lacking, despite a general understanding of the biochemical basis of SLT‐1 toxicity. Here we present evidence that the mechanism by which the catalytic domain of RIPs cleaves its substrate involves initial docking interactions with the ribosomal stalk by virtue of a conserved C‐terminal domain common to all three stalk proteins P0, P1, and P2. The A1 chain of SLT‐1 transiently binds to this peptide with a modest binding constant and rapid on and off rates. Mutagenesis of charged residues within the A1 chain identified a cationic surface that interacts with the peptide motif. In addition, peptide phage‐display revealed a complementary charged surface and an additional hydrophobic motif which may be involved in the interaction. Moreover, deletion mutagenesis performed on the ribosomal protein P0 revealed that the A1 chain binds to an alternate site on P0 in proximity to the contact sites for P1/P2 heterodimers. These results demonstrate that the catalytic chain of RIPs such as SLT‐1 dock on ribosomes using two classes of binding sites located within the ribosomal stalk which may aid in orienting their catalytic domain in close proximity to the depurination site.