Protein Folding Activity of Ribosomal RNA Is a Selective Target of Two Unrelated Antiprion Drugs

Abstract

Background6-Aminophenanthridine (6AP) and Guanabenz (GA, a drug currently in use for the treatment of hypertension) were isolated as antiprion drugs using a yeast-based assay. These structurally unrelated molecules are also active against mammalian prion in several cell-based assays and in vivo in a mouse model for prion-based diseases.Methodology/Principal FindingsHere we report the identification of cellular targets of these drugs. Using affinity chromatography matrices for both drugs, we demonstrate an RNA-dependent interaction of 6AP and GA with the ribosome. These specific interactions have no effect on the peptidyl transferase activity of the ribosome or on global translation. In contrast, 6AP and GA specifically inhibit the ribosomal RNA-mediated protein folding activity of the ribosome.Conclusion/Significance6AP and GA are therefore the first compounds to selectively inhibit the protein folding activity of the ribosome. They thus constitute precious tools to study the yet largely unexplored biological role of this protein folding activity.

The Antiprion Compound 6-Aminophenanthridine Inhibits the Protein Folding Activity of the Ribosome by Direct Competition

“…Is PFAR functional in the modern cells, or is it an evolutionary relic representing function of an ancient protein production machine? Although there are few reports of PFAR in living bacterial cells (14,15), the in vivo context of PFAR has not been fully established. However, one recent finding has linked PFAR to living cells and also associated it with diseases of higher eukaryotes.…”

“…However, one recent finding has linked PFAR to living cells and also associated it with diseases of higher eukaryotes. It has been shown that the two unrelated compounds 6-aminophenanthridine (6AP) and guanabenz acetate, with demonstrated activity against yeast ([PSI ϩ ] and [URE3]) and mammalian prions, bind to rRNA and inhibit PFAR (15)(16)(17). The correlation between the antiprion activity of these two drugs and their ability to specifically inhibit PFAR suggests that PFAR could be involved in the establishment or maintenance of the prion processes in cells.…”

“…The correlation between the antiprion activity of these two drugs and their ability to specifically inhibit PFAR suggests that PFAR could be involved in the establishment or maintenance of the prion processes in cells. This notion was further reinforced by the discovery that a 6AP derivative called 6APi, in which the 6-amino group of 6AP is substituted with 2-butan-1-ol, was inactive in both the reversion of the prion phenotype in vivo and inhibition of PFAR in vitro (15). In a different context, PFAR was suggested to be involved in another amyloid-based disease, oculopharyngeal muscular dystrophy, which is an inherited myodegenerative disease caused by the aggregation of PABPN1 protein into amyloid fibers within the nucleus of muscle cells (18).…”

“…The third column represents degree of defect (100% Ϫ refolding efficiency). (15,20). Based on the refolding kinetics, it was suggested that 6AP competes with the protein substrates for the binding sites on rRNA, although direct proof in support of this claim was unavailable (20).…”

Chémobiologie à l’happy hour

“…L'approche la plus fructueuse fut la chromatographie d'affinité sur composés immobilisés sur des billes de Sépharose®. Cette approche nous a permis d'identifier l'activité chaperon de protéines du ribosome (PFAR, protein folding activity of the ribosome) comme nouvel acteur potentiel de la « prionisation », et donc comme cible thérapeutique potentielle pour traiter ces maladies [27][28][29]. Tous travailler avec le prion de mammifère, les prions de levure peuvent être manipulés sans précaution particulière du fait de leur innocuité.…”