Leucine 232 and hydrophobic residues at the ribosomal P stalk binding site are critical for biological activity of ricin.

Leucine 232 and hydrophobic residues at the ribosomal P stalk binding site are critical for biological activity of ricin. Biosci Rep. 2019 Sep 23;: Authors: Zhou Y, Li XP, Kahn JN, McLaughlin JE, Tumer NE Abstract Ricin interacts with the ribosomal P stalk to cleave a conserved adenine from the a-sarcin/ricin loop (SRL) of the rRNA. Ricin toxin A chain (RTA) uses Arg235 as the most critical arginine for binding to the P stalk through electrostatic interactions to facilitate depurination. Structural analysis showed that a P2 peptide binds to a hydrophobic pocket on RTA and the last two residues form hydrogen bonds with Arg235. The importance of hydrophobic residues relative to Arg235 in the interaction with the P stalk in vivo and on the toxicity of RTA is not known. Here, we mutated residues in the hydrophobic pocket to analyze their contribution to toxicity and depurination activity in yeast and in mammalian cells. We found that Leu232, Tyr183 and Phe240 contribute cumulatively to toxicity, with Leu232 being the most significant. A quadruple mutant, Y183A/L232A/R235A/F240A, which combined mutations in critical hydrophobic residues with R235A completely abolished the activity of RTA, indicating that Arg235 and hydrophobic residues are required for full biological activity. Y183A and F240A mutants had reduced activity on RNA, but higher activity on ribosomes compared to R235A in vitro , suggesting that they could partially regain acti...
Source: Bioscience Reports - Category: Biomedical Science Authors: Tags: Biosci Rep Source Type: research