Effects of Phospholipids on the Aggregation Behaviors of β-amyloid Peptide and its Mutant
Date Issued
2010
Date
2010
Author(s)
Lin, Keng-Chi
Abstract
Previous studies have proved that the hydrophobic β-amyloid peptide (Aβ), the major proteinacious constituent of senile plaques, is the product of β-amyloid precursor protein cutting by two different enzymes. Due to the effects of various environmental factors, the released Aβ may aggregate and induce cytotoxicity to cause Alzheimer’s disease. In addition, findings from the genetic researches indicate that there are two forms of Alzheimer’s disease, sporadic and familial forms, and evidence shows that the mechanisms of aggregation behavior for these two forms are significantly different.
Given that β-amyloid precursor protein is one of the transmembrane proteins, cell membrane is evidently closely correlated with either the initial structure inside the membrane before cutting by enzymes or the resultant Aβ species released into the extracellular environment. The aforesaid membrane-protein interaction is evidenced to be influenced by the charge, composition, and fluidity of membrane.
With two types of phospholipids, 1,2-dimyristoyl-sn-glycerol-3-phosphocholine (DMPC) and 1,2-diheptanoyl-sn-glycero-3-phosphocholine (di-C7-PC), used as the model systems, the current study was aimed to explore the effects of phospholipid molecules on β-amyloid peptides experimentally and theoretically. We first used E.coli as the host cells to express and purify our target peptides, wild-type Aβ(1-40) and Arctic Aβ(1-40). The molecular mass of the purified peptide was verified by MALDI-TOF mass spectrometry. The yields for wild-type Aβ(1-40) and Arctic Aβ(1-40) were found to be ~4 mg/L and ~2 mg/L, respectively. In the second part, we found that the rate of fibrillization and the changes of protein structure were positively correlated with the concentration of added di-C7-PC. The highest rate of fibrillization and the most marked transition of protein structure were observed upon addition of 5 mM di-C7-PC. In addition, our 100ns molecular dynamic simulations results demonstrated that, in both wild-type Aβ(1-40) and Arctic Aβ(1-40), the changes in peptides structures (secondary and tertiary structures) and system energy were highly affected by the concentration of phospholipids. We also found that the pronounced influence was detected in Arctic Aβ(1-40) containing a higher concentration of di-C7-PC. Finally, we used Aβ(1-60) as a model of C99 inside the membrane to gain the initial structure information by molecular dynamics simulations. The results showed that wild-type Aβ(1-60) has higher stability than that of Arctic Aβ(1-60) when staying inside the transmembrane domain. In addition, the secondary structure analysis revealed that the unfolding behavior occurred within the range of residues 40-42 during the simulation time of 100 ns.
In summary, through various experimental measurements and molecular dynamics simulations, we conclude in this study that cell membrane evidently plays an important role during the transition of protein structure. We believe the results reported here may contribute to our better understanding of the difference between β-amyloid peptide and its mutant in regards to the aggregation behaviors and the molecular mechanisms of Aβ-lipid interactions.
Subjects
wild-type and mutation β-amyloid peptide
amyloid fibrils
phospholipids
molecular dynamics simulations
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-99-R97524061-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):00d5669847d11c3fb79fabb250264965