Structure And Dynamics Of The Protective Mutant G127V Of Human Prion Protein

Human prion protein is endogenous and glycosylphosphatidylinositol anchored membrane protein encoded by endogenous prion protein gene(PRNP)located at 20th chromosome.Conformational conversion of prion protein from cellular prion protein(PrPc)with a helices primarily to scrapie isoform(PrPSc)with ?-sheet principally is the pathogenesis for prion diseases,also known as Transmissible Spongiform Encephalopathies(TSEs).These deseases are a type of neurodegenerative diseases which destroy the central nervous system(CNS).In human sapiens,prion diseases manifest as a variety of clinical symptoms:Creutzfeldt-Jakob diseases(CJD,including sporadic,iatrogenic,variant,and familial/genetic CJD),Gerstmann-Straussler-Scheinker syndrome(GSS),Fatal Familial Insomnia(FFI)and Kuru.These deseases possess long latency,lack effective early diagnosis and treatment,and 100%mortality rate.Till now,more than 50 pathogenic point-mutations of PRNP have been identified to be associated with a variety of prion diseases.Fortunately,a completely prion disease-resistant mutant G127V has also been identified in bodies of Papua New Guinea's Fore and verified in transgenic mice studies,especially homozygote of V127.However,the underlying disease-resistance mechanisms remain elusive.To dissect the molecular mechanism of the resistance,the high resolution solution structure of G127V of recombinant human prion protein(residues 91-231)was determined.Significantly in HuPrP(G127V),the segments of residue Tyr128-Gly131 and Val161-Arg164 can't form anti-parallel ?-sheet stably,but assemble to Stretch-Strands pattern(SSs)with extending atomic distances between the two strands.The al helix is extended to Arg156,and packed tightly with banded a2 and a3 helices.In addition,the region around the residues Gly 126-Serl 35 is distributed neutral potentials.In details,the phenyl ring of Tyr128 is rotated sharply with dihedral angle chi(N-Ca-C?-C?)change,and is away from Ile 182 and close to Gln 186.Because of stereospecific blockade of Val127,the interaction between the si dechains of Arg164 and Asp 178 has been strengthened.Due to turning around the dihedral angle of psi(Tyr157),the pyrrolidine of Pro158 has retroflexed and change the cavities among of three a helices and ?1-SS2 loop.Overall,compared to WT HuPrP,the alteration of the structure for HuPrP(G127V),especially SSs,might be the structural basis of protective function.Furthermore,NMR dynamics is employed to analysis the intramolecular motion for help understanding the mechanism of resistance.In HuPrP(G127V),the residue Gly131 exhibited a large values of transverse relaxation rates(R2)and low-frequency spectral density function J(0).The CPMG relaxation dispersion confirmed that Gly131 behaved ?s-ms timescales conformational exchange.Moreover,Tyr 128 and Tyr 163 located at SSs also exhibited conformational exchanges.Additionally,Gln172 and Gln186 exhibited ?s-ms timescales motion but Ile 182 not.Interestingly,the a3 helix displayed a fluctuation at the magnetic strength field of 19.97 T but not at 14.10 T.At the end,the proton exchange experiment verified that the amide proton of Gly131 was easily to be exchanged.All of dynamics properties of HuPrP(G127V)are the dynamic basis for the protective function.Moreover,molecular dynamics(MD)simulation is hired to analysis the intramolecular and intermolecular motion.In the structure of HuPrP(G127V),SSs was stably on 0-100 ns timescales evolution and did not convert into ?-sheet.The ?1 helix was extended with 310 helix.The distance between mass centers of Val127 and Pro165 has been decreased.Due to the Val127,the sidechain of Tyrl28 rotated to "out" of the SSs and displayed "mediate" conformation sometime.Because of stereospecific blockade of Tyrl28,intermolecular hydrogen bond did not be formed between HuPrP(G127V)and other prion proteins.After then,the dimerization or aggregation has been prohibited.Totally,MD simulation also confirmed that the SSs of HuPrP(G127V)is the dynamic basis for the protective function.In summary,through NMR and MD simulation,our works provided the unique dynamic structural features for HuPrP(G127V).These features might be responsible for prion disease-resistance effect of the G127V mutant.This work may be also helpful for mechanistically understanding the pathogenesis of prion diseases and developing effective drugs against prion diseases.