Determine the Orientation of β-Sheet Conformation for Specific Residues in N-Terminus of α-syn(61－95) in Monolayer by pMAIRS

Abstract

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, and the hallmark of PD is the presence of Lewy bodies in the midbrain. The protein component of Lewy bodies is α-synuclein, a protein that consists of 140 amino acids. The sequence of α-synuclein can be divided into three distinct domains, namely, the N-terminus domain, the non-amyloid component domain or NAC, and the C-terminus domain. The NAC domain, which consists of residues 61-95, has been of utmost importance due to the disordered self-assembly behavior. In addition, NAC and other segment peptides have been detected in Lewy bodies. Previously in our research group, NAC was investigated by p-Polarized Multiple Angle Incidence Resolution Spectroscopy (pMAIRS) which can be used to detect the orientation of various vibrations in ultrathin films (such as monolayer). The overall conformation of NAC in a freshly prepared monolayer structure was shown to be α-helix. In addition, 13C isotopic label has been introduced into residue 93C in NAC. By pMAIRS, the orientation of the α-helix at 93G is parallel to the interface. In this thesis, the monolayer of NAC was compressed for several days, and β-sheet conformation was detected in the monolayer of NAC. By introducing 13C isotopic label into the other residues in the sequence of NAC, 93G was found to be still in α-helix after three days of compression. However, the N-terminus residue (68G) changed its conformation from α-helix to β-sheet after three days of compression. Moreover, 63V which is closer to the N-terminus changed its conformation after only two days of compression. Furthermore, edge-up orientation was detected for the newly generated β-sheet conformation. Therefore, the capability of pMAIRS to analyze the structure of membrane proteins in a monolayer with residue-level resolution was demonstrated.