Interdisciplinary PhD in Molecular Biosciences

Dr. Chengshan Wang - Research Interests

Parkinson's disease (PD) is characterized by the abnormal intracellular inclusions, namely, Lewy bodies, which is composed of lipids and α-synulcien (α-syn). α-Syn, a protein with 140 amino acids, is unstructured in aqueous solution and in vitro can form fibrils in β-sheet conformation which is identical to that detected in Lewy bodies. α-Syn is a 140-amino-acid presynaptic protein (shown in Scheme 1) and the sequence can be divided into three regions, namely, the positively charged N-terminus (residues 1-60), the aggregation-prone nonamyloid components (NAC, residues 60-95), and the negatively charged C-terminus (residues 95-140). My research interests focus on the biophysical characters of α-syn as summarized below.

MDVFMKGLSK AKEGVVAAAE KTKQGVAEAA GKTKEGVLYV GSKTKEGVVH
GVATVAEKTK
EQVTNVGGAV VTGVTAVAQK TVEGAGSIAA ATGFV KKDQL
GKNEEGAPQE GILEDMPVDP DNEAYEMPSE EGYQDYEPEA


Scheme 1. The sequence of α-synuclein with the N-terminus underlined and the C-terminus expressed in Italics.

  1. Clarify the structure of α-syn aggregates in residue level.
    Clarification of protein structure is important to address both the function of protein and the mechanism how protein works in vivo. Although X-ray crystallography is a powerful technique to elucidate the protein structure in atomic level, this technique is still limited because a large number of proteins cannot form single crystal structure. α-Syn is one of the non-crystal proteins and the structure of α-syn aggregates has been indicated to be difficult to elucidated by X-ray crystallography. Since the structure of α-syn aggregates is important for both PD pathology and drug development, a methodology which can resolve the structure will be welcome.

    Recently, residue-level peptide/protein structure has been elucidated by the detection of amide I band (between 1700 to 1590 cm -1) in infrared (IR) spectroscopy when the peptide/protein is C13 labeled. For example, the regular amide I band appears at 1620 cm 1 in β-sheet conformation because of the hydrogen bond formation between the amide groups in neighboring strands. Whereas the C13 labeled residue will show the amide I band at 1600 cm-1 when forming H-bond with regular C12 residues in the neighboring peptide chain. As the NAC part of α-syn has been shown to be responsible for the aggregation, my first project will focus on synthesize C13 labeled segment peptides of α-syn and clarify the structure of α-syn aggregates.
  2. Study the lipid interaction with α-syn at the air-water interface.
    Although the aggregation of unstructured α-syn has been well studied, α-syn accumulates in the presynaptic terminals where exists high density of vesicles. α-Syn changes its conformation to α-helix in the presence of vesicles and we found that this conformation change is irreversible. Thus, the accumulation of α-syn may be due to the vesicles in presynaptic terminals and the accumulated α-syn may be extensively in α-helix in vivo. Although the aggregation of α-syn in the presence of vesicles has attracted scientific interest, controversy results have been reported possibly because the nature of α-syn interaction with phospholipids is difficult to be addressed by vesicle system.

    g - Research Interests The difficulty is due to the instinct isotropic character of vesicle. For instance, the orientation of alkyl chains in vesicles is distributed evenly in all directions due to the spherical shape of vesicles. Therefore, the orientation change of alkyl chains in the absence and presence of α-syn is difficult to be detected. Similarly, although α-syn has been reported to orient parallel to the vesicles surface, the sphere surface of vesicle may make the orientation of α-syn randomly distributed. Consequently, the orientation change of α-syn in the presence of phospholipids with various headgroups and alkyl chains is also difficult to compare. Thus, an anisotropic system which can also mimic membrane structure in vivo may help to clarify the nature of α-syn interaction with phospholipids and evaluate the interaction effect on the aggregation of α-syn.

    Langmuir monolayer technique can build up a phospholipid monolayer identical to half of cell membrane and consequently, has been widely used as model to study biophysical characters of cell membrane (shown in Scheme 2). Different to vesicles system, Langmuir monolayer is very sensitive about the molecular interaction between neighboring lipids or between lipids molecule with other molecules (e.g., proteins/peptides) in the water phase by measuring the surface pressure-area (π-A) isotherm. Furthermore, the Langmuir monolayer is anisotropic and the recently developed Infrared Reflection-Absorption Spectroscopy (IRRAS) has been proved to be a powerful technique to detect the order and orientation of the alkyl chains of phospholipids as well as the orientation change of proteins in the subphase without additional probes. My second research interest focuses on the employment of Langmuir monolayer and IRRAS techniques to study the nature of the α-syn interaction with phospholipids. As to our knowledge, no paper has been published to clarify either the α-syn interaction with phospholipids by Langmuir monolayer technique or the interaction effect on α-syn aggregation.

Scheme 2. Illustration of Langmuir monolayer and IRRAS techniques.