Журнал хроматографии и методов разделения
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Role of Different Regions of α-synuclein in the Interaction with the Brain Fatty Acid DHA

Giorgia De Franceschi and Patrizia Polverino de Laureto

α-Synuclein is a protein involved in Parkinson’s disease. Its interaction with brain polyunsaturated fatty acids is attracting a strong interest. Previously, we investigated the interaction ofα-syn with docosahexaenoic acid (DHA), and a mutual effect between the monomeric protein and the fatty acid was observed. α-Syn acquires an α-helical secondary structure with a rapid equilibrium between its free and the lipid bound form. In the α-helical form the protein segment 73-102 is flexible and is not characterized by a persistent structure. DHA forms oil droplets in the presence of the protein. To investigate at molecular level the involvement of different regions of the protein in the interaction with DHA, truncated protein species were prepared (syn1-99, syn1-52, syn57-102 and syn108-140) and their ability to interact with DHA was analyzed by circular dichroism and proteolytic mapping. CD data showed that all the peptides, except that corresponding to the C-terminal region, are able to acquire alpha-helical structure in the presence of DHA. The different molar ratio polypeptide/DHA necessary to reach the maximum folding and the different final helix content between the two N-terminal peptides (syn1-99, syn1-52) and the NAC peptide (syn57- 102) suggest that the sequence repeats plays an important role in the α-helix transition and thereby in the interaction with DHA. The proteolysis experiments showed that all the truncated species are resistant to proteolysis in the presence of saturating concentrations of DHA, indicating that almost all the residues are engaged in the interaction with the lipid. The C-terminal region, at variance, seems only to modulate the portion of the molecule buried into the lipid compartment. Moreover the ability of the peptides to affect the self-assembly of the fatty acid was also analyzed showing that the peptides that interact also change the physical state of DHA, by the positive charged N-terminus.