Species-specific inhibition of fungal protein synthesis by sordarin: identification of a sordarin-specificity region in eukaryotic elongation factor 2

The sordarin class of natural products selectively inhibits fungal protein synthesis by impairing the function of eukaryotic elongation factor 2 (eEF2 ). Mutations in Saccharomyces cerevisiae eEF2 or the ribosomal stalk protei n rpP0 can confer resistance to sordarin, although eEF2 is the major determ inant of sordarin specificity. It has been shown previously that sordarin s pecifically binds S. cerevisiae eEF2 while there is no detectable binding t o eEF2 from plants or mammals, despite the high level of amino acid sequenc e conservation among these proteins. In both whole-cell assays and in vitro translation assays, the efficacy of sordarin varies among different specie s of pathogenic fungi. To investigate the basis of sordarin's fungal select ivity, eEF2 has been cloned and characterized from several sordarin-sensiti ve and -insensitive fungal species. Results from in vivo expression of Cand ida species eEF2s in S. cerevisiae and in vitro translation and growth inhi bition assays using hybrid S. cerevisiae eEF2 proteins demonstrate that thr ee amino acid residues within eEF2 account for the selectivity of this clas s of compounds. It is also shown that the corresponding residues at these p ositions in human eEF2 are sufficient to confer sordarin insensitivity to S cerevisiae identical to that observed with mammalian eEF2.