Mechanism For The Effect Of Unique Substitution Of Codon 177 On Dog Prion Protein Misfolding

Prion diseases,also known as transmissible spongiform encephalopathies(TSEs),are incurable and fatal neurodegenerative conditions affecting humans and some other mammals.Prion,an infectious protein factor,is the pathogenic agent of TSEs and consists primarily of Pr P^Sc,the pathological aggregates of the cellular prion protein(Pr P^C).Prions have been responsible for widespread disease epidemics,including kuru in humans,bovine spongiform encephalopathy(BSE)in cattle,and chronic wasting disease(CWD)in cervids.Although the most mammals are sensitive to the infection of prions,some species including rabbits,equids,and canines have been reported to resist TSEs.The prion-resistant ability is likely to be hidden in the unique prion protein(Pr P)sequences of rabbits,equids,and canines.For example,dog Pr P contains two unique mutations,Asp159 and Arg177.Asp159 is not only a key amino acid site responsible for its own resistance to Pr P misfolding,but also significantly inhibits Pr P^Sc formation after introducing N159D substitution on mouse Pr P^C,having an important protective effect.However,the function of another unique substitution of codon 177 is still unknown,and whether it has a similar protective effect needs further investigation.In this study,we hope to determine whether the unique substitution of codon 177 has a protective effect on Pr P misfolding.We show that the introduction of R177H substitution on dog Pr P significantly accelerated its fibril formation and decreased its stability.On the contrary,the aggregation ability of H177R was significantly lower than that of wild-type human Pr P.Furthermore,R177H significantly enhanced the accumulation of cellular,insoluble dog Pr P aggregates,suggesting that R177substitution is able to prevent Pr P conformational change and pathogenesis.Additionally,the variant H177R significantly prevented the aggregation of human Pr P in cells and protected against the increase in ROS and cytotoxicity induced by Pr P 106-126.We thus conclude that the unique substitution of codon 177 on Pr P misfolding plays an important role in maintaining its stability and the protective effect of R177might be responsible for the prion resistance of canines.