Structural insights into the interaction of the ribosomal P stalk protein P2 with a type II ribosome-inactivating protein ricin

摘要

Ricin is a type II ribosome-inactivating protein (RIP) that depurinates A⁴³²⁴ at the sarcin-ricin loop of 28 S ribosomal RNA (rRNA), thus inactivating the ribosome by preventing elongation factors from binding to the GTPase activation centre. Recent studies have disclosed that the conserved C-terminal domain (CTD) of eukaryotic ribosomal P stalk proteins is involved in the process that RIPs target ribosome. However, the details of the molecular interaction between ricin and P stalk proteins remain unknown. Here, we report the structure of ricin-A chain (RTA) in a complex with the CTD of the human ribosomal protein P2. The structure shows that the Phe¹¹¹, Leu¹¹³ and Phe¹¹⁴ residues of P2 insert into a hydrophobic pocket formed by the Tyr¹⁸³, Arg²³⁵, Phe²⁴⁰ and Ile²⁵¹ residues of RTA, while Asp¹¹⁵ of P2 forms hydrogen bonds with Arg²³⁵ of RTA. The key residues in RTA and P2 for complex formation were mutated, and their importance was determined by pull-down assays. The results from cell-free translation assays further confirmed that the interaction with P stalk proteins is essential for the inhibition of protein synthesis by RTA. Taken together, our results provide a structural basis that will improve our understanding of the process by which ricin targets the ribosome, which will benefit the development of effective small-molecule inhibitors for use as therapeutic agents.