Conformation and topology of amyloid β-protein adsorbed on a tethered artificial membrane probed by surface plasmon field-enhanced fluorescence spectroscopy

Progressive depositions of cerebral amyloid are primary neuropathologic features of Alzheimer’s disease (AD). The amyloid is composed of a 39–42 amino acid peptide called the amyloid β-protein (Aβ). Repeated investigation suggests that the conformational transition of Aβ from α-helix or random coil to β-sheet structure plays a key role in the inappropriate accumulation of cerebral amyloid plaques. In this manuscript, we describe a fluorescence-based immunoassay technology to investigate the conformation and topology of Aβ peptides interacting with peptide–tethered planar lipid bilayers. Dual monoclonal antibodies (mAbs) labelled with fluorophores were employed to recognise a linear N- and a β-sheet C-terminus of Aβ peptides on the model membrane, respectively. Kinetics of antibody-Aβ binding were determined by surface plasmon field-enhanced fluorescence spectroscopy (SPFS). The conformational transition of Aβ by melatonin, a defined β-sheet breaker, was probed using paired monoclonal antibodies. The Aβ interaction with the membrane was evaluated by carefully analyzing the change in kinetic/affinity parameters in the presence or absence of melatonin. These results show that SPFS can be used to examine conformational transition of Aβ on an artificial membrane, providing a novel and versatile platform for conveniently monitoring protein-membrane interaction and screening for new β-sheet breakers.