Studies of interactions of sphingolipid-interacting peptides and liposomes with surface plasmon resonance.

Abstract

Special micro domains on cell membranes, known as lipid rafts, contain a high content of sphingolipid and cholesterol. They are preferential sites for the binding of peptides or proteins such as toxins and Amyloid Beta (Aβ) in order to gain entry into the cell. Interactions between these lipid rafts and Aβ are crucial in Aβ aggregation and fibril formation, which cause Alzheimer’s disease (AD) in humans. In this report, we focused on the sphingolipid binding domain (SBD) of Aβ1-25, which interacts with sphingolipids on lipid rafts and is used by as a marker in sphingolipid-rich domains. The interactions between SBDs and the trisialoganglioside GT1b were characterized using Surface Plasmon Resonance (SPR) biosensor technology. The original SBD sequence was modified by substituting a lysine residue to glutamic acid at the 16th amino acid on the SBD. Higher binding affinity was observed for the K16 version, which occurs in human Aβ naturally, on liposomes with GT1b, while there were no significant differences in the binding affinities of E16 SBD on liposomes with and without GT1b. K16 requires GT1b to bind with high affinity. We propose that this interaction depends at least partly on charged interactions, which are disrupted by substitution of the oppositely charged E16 residue for K16.