Lipid‐induced conformational transition of the amyloid core fragment Aβ(28–35) and its A30G and A30I mutants

Abstract

The interaction of the b-amyloid peptide (Ab) with neuronal membranes could play a key role in the pathogenesis of Alzheimer's disease. Recent studies have focused on the interactions of Ab oligomers to explain the neuronal toxicity accompanying Alzheimer's disease. In our study, we have investigated the role of lipid interactions with soluble Ab(28-35) (wild-type) and its mutants A30G and A30I in their aggregation and conformational preferences. CD and Trp fluorescence spectroscopic studies indicated that, immediately on dissolution, these peptides adopted a random coil structure. Upon addition of negatively charged 1,2-dipalmitoylsyn-glycero-3-phospho-rac-(glycerol) sodium salt (PG) lipid, the wild-type and A30I mutant underwent reorganization into a predominant b-sheet structure. However, no conformational changes were observed in the A30G mutant on interaction with PG. In contrast, the presence of zwitterionic 1,2-dipalmitoyl-syn-glycero-3-phosphatidylcholine (PC) lipid had no effect on the conformation of these three peptides. These observations were also confirmed with atomic force microscopy and the thioflavin-T assay. In the presence of PG vesicles, both the wild-type and A30I mutant formed fibrillar structures within 2 days of incubation in NaCl ⁄ P i , but not in their absence. Again, no oligomerization was observed with PC vesicles. The Trp studies also revealed that both ends of the three peptides are not buried deep in the vesicle membrane. Furthermore, fluorescence spectroscopy using the environment-sensitive probe 1,6-diphenyl-1,3,5-hexatriene showed an increase in the membrane fluidity upon exposure of the vesicles to the peptides. The latter effect may result from the lipid head group interactions with the peptides. Fluorescence resonance energy transfer experiments revealed that these peptides undergo a random coil-tosheet conversion in solution on aging and that this process is accelerated by negatively charged lipid vesicles. These results indicate that aggregation depends on hydrophobicity and propensity to form b-sheets of the amyloid peptide, and thus offer new insights into the mechanism of amyloid neurodegenerative disease.

Lipids in Amyloid-β Processing, Aggregation, and Toxicity

“…In contrast, zwitterionic phospholipids, such as phosphatidylcholine (PC) or sphingomyelin, were reported in some studies to show very weak or no interaction with Aβ peptides and induce little if any ordered secondary structure (Terzi et al 1997 ;Chauhan et al 2000 ;Matsuzaki 2007 ;Chi et al 2008 ;Nagarajan et al 2008 ). In contrast, other studies showed signifi cant effects of PCs on the secondary structure and aggregation of Aβ; this includes our own work described in Sect.…”

“…Numerous biophysical studies have demonstrated that lipids and lipid-mimicking detergents can importantly infl uence the secondary structure of Aβ and its aggregation and fi brillation in vitro. Thus, studies using NMR, circular dichroism, Fourier transform infrared spectroscopy, molecular dynamics simulations and fl uorescence spectroscopy have demonstrated Aβ interactions with vesicles containing anionic phospholipids such as phosphatidylglycerol (Terzi et al 1997 ;McLaurin et al 1998 ;Nagarajan et al 2008 ), as well as with other lipid assemblies such as bilayers, micelles or ganglioside clusters (Matsuzaki and Horikiri 1999 ;Mandal and Pettegrew 2004 ;Xu et al 2005 ;Matsuzaki 2007 ;Miyashita et al 2009 ;Matsuzaki et al 2010 ), and showed that these interactions can alter the secondary and/or the quaternary structure of the peptide.…”

Lipid-Induced Conformational Transition of Amyloid β Peptide Fragments

“…Increase in ThT fluorescence with time (days/h) was plotted mutant, an increase in energy transfer was noted upon binding to PG vesicles, as indicated by a decrease in Trp fluorescence intensity and a concurrent increase in dansyl fluorescence emission intensity. In a recent report, we have provided one possible explanation for the observed increase in energy transfer in the case of PG vesicles (Nagarajan et al 2008). Briefly, in the case of the E22G mutant, aggregation occurs in an alternative manner due to the spontaneous formation of β-sheet aggregates bound to the membrane.…”

Density functional theory analysis and spectral studies on amyloid peptide Aβ(28–35) and its mutants A30G and A30I

“…Ab (28)(29)(30)(31)(32)(33)(34)(35) having the sequence KGAIIGLM is a particularly attractive system as it is the key hydrophobic region and forms a rigid amyloid core of the full length Ab (Ippel et al, 2002). In a recent work (Nagarajan et al, 2008), we have examined the role of lipid interactions with soluble Ab(28-35) and its mutants A30G and A30I in their aggregation and conformational preferences. CD and Trp fluorescence spectroscopic studies reveal that these peptides adopt a random coil structure, immediately on dissolution.…”