Trp221 is involved in the protective effect of elongation factor eEF-2 on the ricin/alpha-sarcin site of the ribosome.

Abstract

Elongation factor eEF-2 treated by N-bromosuccinimide under conditions which oxidize 2 Trp residues (Trp343 and Trp221) is inactivated in ribosome-dependent GTP hydrolysis and polyphenylalanine synthesis, and inactivation correlates with the specific oxidation of Trp221 (Guillot, D., Penin, F., Di Pietro, A., Sontag, B., Lavergne, J. P., and Reboud, J. P. (1993) J. Biol. Chem. 268, 20911-20916). It is shown here that this oxidation prevents neither GTP binding to eEF-2 nor the formation of the ribosome-eEF-2-GPP(NH)P complex, but that oxidized eEF-2 is no longer able to protect ribosomes against ricin inactivation. These observations suggest that Trp221 or an amino-acid sequence containing this residue interacts with the 28 S rRNA loop including the GAGA sequence, which is the target of ricin. Such a hypothesis is discussed in relation with data on RNA recognition motifs described in different proteins.