Synuclein Proteins of the Pufferfish <i>Fugu rubripes</i>:  Sequences and Functional Characterization^†

Abstract

In humans, three genes encode the related α-, β-, and γ-synucleins, which function as lipid-binding proteins in vitro. They are being widely studied, mainly because of the central involvement of α-synuclein in a number of neurodegenerative diseases, including Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. In these diseases, the normally soluble α-synuclein assembles into abnormal filaments. Here, we have identified and characterized the synuclein gene family from the pufferfish Fugu rubripes. It consists of four genes, which encode α-, β-, γ1-, and γ2-synucleins. They range from 113 to 127 amino acids in length and share many of the characteristics of human synucleins, including the presence of imperfect amino-terminal repeats of 11 amino acids, a hydrophobic middle region, and a negatively charged carboxy-terminus. All four synucleins are expressed in the Fugu brain. Recombinant Fugu synucleins exhibited differential liposome binding, which was strongest for α-synuclein, followed by β-, γ2-, and γ1-synucleins. In assembly experiments, Fugu α-, γ1-, and γ2-synucleins formed filaments more readily than human α-synuclein. Fugu β-synuclein, by contrast, failed to assemble in bulk. Filament assembly of synucleins was directly proportional to their degree of hydrophobicity and their tendency to form β-sheet structure, and correlated inversely with their net charge