Domain Swapping in p13suc1 Results in Formation of Native-like, Cytotoxic Aggregates

The field of protein aggregation has been occupied mainly with the study of β-strand self-association that occurs as a result of misfolding and leads to the formation of toxic protein aggregates and amyloid fibers. However, some of these aggregates retain native-like structural and enzymatic properties suggesting mechanisms other than β-strand assembly. p13suc1 is a small protein that can exist as a monomer or a domain-swapped dimer. Here, we show that, under native conditions, p13suc1 forms three-dimensional domain-swapped aggregates, and that these aggregates are cytotoxic. Thus, toxicity of protein aggregates is not only associated with β-rich assemblies and amyloid fibers, involving non-native interactions, but it can be induced by oligomeric misassembly that maintains predominantly native-like interactions.