National Center for
4HMM: Crystal Structure Of Mutant Rabbit Prp 121-230 (s174n)
N-Terminal Helix-Cap in alpha-Helix 2 Modulates beta-State Misfolding in Rabbit and Hamster Prion Proteins
PLoS ONE (2013) 8 p.E63047
Susceptibility of a particular species to prion disease is affected by small differences in the sequence of PrP and correlates with the propensity of its PrP to assume the beta-state. A helix-cap motif in the beta2-alpha2-loop of native alpha-helical rabbit PrP, a resistant species, contains sequence differences that influence intra- and interspecies transmission. To determine the effect the helix-cap motif on beta-state refolding propensity, we mutated S170N, S174N, and S170N/S174N of the rabbit PrP helix-cap to resemble that of hamster PrP and conversely, N170S, N174S, and N170S/N174S of hamster PrP to resemble the helix-cap of rabbit PrP. High-resolution crystal structures (1.45-1.6 A) revealed that these mutations ablate hydrogen-bonding interactions within the helix-cap motif in rabbit PrP(C). They also alter the beta-state-misfolding propensity of PrP; the serine mutations in hamster PrP decrease the propensity up to 35%, whereas the asparagine mutations in rabbit PrP increase it up to 42%. Rapid dilution of rabbit and hamster into beta-state buffer conditions causes quick conversion to beta-state monomers. Kinetic monitoring using size-exclusion chromatography showed that the monomer population decreases exponentially mirrored by an increase in an octameric species. The monomer-octamer transition rates are faster for hamster than for rabbit PrP. The N170S/N174S mutant of hamster PrP has a smaller octamer component at the endpoint compared to the wild-type, whereas the kinetics of octamer formation in mutant and wild-type rabbit PrP are comparable. These findings demonstrate that the sequence of the beta2-alpha2 helix-cap affects refolding to the beta-state and subsequently, may influence susceptibility to prion disease.