Solution structure of human P1*P2 heterodimer provides insights into the role of eukaryotic stalk in recruiting the ribosome-inactivating protein trichosanthin to the ribosome.
Lee, Ka-Ming 1; Yusa, Kazuyuki 2; Chu, Lai-On 1; Yu, Conny Wing-Heng 1; Oono, Moe 2; Miyoshi, Tomohiro 2; Ito, Kosuke 2; Shaw, Pang-Chui 1; Wong, Kam-Bo 1,*; Uchiumi, Toshio 2,*
[Miscellaneous Article] Nucleic Acids Research. 41(18):8776-8787, October 2013.

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: Lateral ribosomal stalk is responsible for binding and recruiting translation factors during protein synthesis. The eukaryotic stalk consists of one P0 protein with two copies of P1*P2 heterodimers to form a P0(P1*P2)2 pentameric P-complex. Here, we have solved the structure of full-length P1*P2 by nuclear magnetic resonance spectroscopy. P1 and P2 dimerize via their helical N-terminal domains, whereas the C-terminal tails of P1*P2 are unstructured and can extend up to ~125 A away from the dimerization domains. 15N relaxation study reveals that the C-terminal tails are flexible, having a much faster internal mobility than the N-terminal domains. Replacement of prokaryotic L10(L7/L12)4/L11 by eukaryotic P0(P1*P2)2/eL12 rendered Escherichia coli ribosome, which is insensitive to trichosanthin (TCS), susceptible to depurination by TCS and the C-terminal tail was found to be responsible for this depurination. Truncation and insertion studies showed that depurination of hybrid ribosome is dependent on the length of the proline-alanine rich hinge region within the C-terminal tail. All together, we propose a model that recruitment of TCS to the sarcin-ricin loop required the flexible C-terminal tail, and the proline-alanine rich hinge region lengthens this C-terminal tail, allowing the tail to sweep around the ribosome to recruit TCS.

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