Carbonic anhydrase amyloid fibrils composed of laterally associated protofilaments show reduced cytotoxicity

Abstract

Cytotoxicity of amyloid fibrils has been shown to depend on their structure. However, specific features of toxic and non-toxic amyloids remain unclear. Here we focus on the relationship between structural characteristics of the fibrils and their cytotoxicity. Bovine carbonic anhydrase B (BCAB) serves as the object of this study because its amyloids reduce cell viability. Limited proteolysis and mass spectrometry were used to determine BCAB regions forming the core of amyloid fibrils. Four BCAB mutants with substitutions reducing hydrophobicity in the regions important for amyloid formation were obtained to study the kinetics of aggregation, structural features, and cytotoxicity of the amyloids. We demonstrate that fibrils of WT BCAB, L78A, L139A, and M239A variants display a pronounced toxic effect on eukaryotic cells, while I208A mutation significantly reduces the cell-damaging effect of amyloids. The data obtained conclude that cytotoxicity of BCAB fibrils does not depend on their length, secondary structure, and exposure of hydrophobic groups to the solvent. A distinctive feature of the low-toxic I208A fibrils is their specific morphology characterized by the lateral protofilaments association and formation of fibril-ribbons.