Both the cis-trans equilibrium and isomerization dynamics of a single proline amide modulate ?2-microglobulin amyloid assembly.

ABSTRACT: The human protein ?2-microglobulin (?2m) aggregates as amyloid fibrils in patients undergoing long-term hemodialysis. Isomerization of Pro32 from its native cis to a nonnative trans conformation is thought to trigger ?2m misfolding and subsequent amyloid assembly. To examine this hypothesis, we systematically varied the free-energy profile of proline cis-trans isomerization by replacing Pro32 with a series of 4-fluoroprolines via total chemical synthesis. We show that ?2m's stability, (un)folding, and aggregation properties are all influenced by the rate and equilibrium of Pro32 cis-trans isomerization. As anticipated, the ?2m monomer was either stabilized or destabilized by respective incorporation of (2S,4S)-fluoroproline, which favors the native cis amide bond, or the stereoisomeric (2S,4R)-fluoroproline, which disfavors this conformation. However, substitution of Pro32 with 4,4-difluoroproline, which has nearly the same cis-trans preference as proline but an enhanced isomerization rate, caused pronounced destabilization of the protein and increased oligomerization at neutral pH. More remarkably, these subtle alterations in chemical composition--incorporation of one or two fluorine atoms into a single proline residue in the 99 amino acid long protein--modulated the aggregation properties of ?2m, inducing the formation of polymorphically distinct amyloid fibrils. These results highlight the importance of conformational dynamics for molecular assembly of an amyloid cross-? structure and provide insights into mechanistic aspects of Pro32 cis-trans isomerism in ?2m aggregation.

SUBMITTER: Torbeev VY 

PROVIDER: S-EPMC3864314 | biostudies-literature | 2013 Dec

REPOSITORIES: biostudies-literature