Secondary Structure and Interfacial Aggregation of Amyloid-β(1−40) on Sodium Dodecyl Sulfate Micelles

Abstract

Alzheimer's disease (AD) is characterized by the presence of large numbers of fibrillar amyloid deposits in the form of senile plaques in the brain. The fibrils in senile plaques are composed of 40- and 42-residue amyloid-beta (Abeta) peptides. Several lines of evidence indicate that fibrillar Abeta and especially soluble Abeta aggregates are important in the pathogenesis of AD, and many laboratories have investigated soluble Abeta aggregates generated from monomeric Abeta in vitro. Of these in vitro aggregates, the best characterized are called protofibrils. They are composed of globules and short rods, show primarily beta-structure by circular dichroism (CD), enhance the fluorescence of bound thioflavin T, and readily seed the growth of long fibrils. However, one difficulty in correlating soluble Abeta aggregates formed in vitro with those in vivo is the high probability that cellular interfaces affect the aggregation rates and even the aggregate structures. Reports that focus on the features of interfaces that are important in Abeta aggregation have found that amphiphilic interactions and micellar-like Abeta structures may play a role. We previously described the formation of Abeta(1-40) aggregates at polar-nonpolar interfaces, including those generated at microdroplets formed in dilute hexafluoro-2-propanol (HFIP). Here we compared the Abeta(1-40) aggregates produced on sodium dodecyl sulfate (SDS) micelles, which may be a better model of biological membranes with phospholipids that have anionic headgroups. At both HFIP and SDS interfaces, changes in peptide secondary structure were observed by CD immediately when Abeta(1-40) was introduced. With HFIP, the change involved an increase in predominant beta-structure content and in fluorescence with thioflavin T, while with SDS, a partial alpha-helical conformation was adopted that gave no fluorescence. However, in both systems, initial amorphous clustered aggregates progressed to soluble fibers rich in beta-structure over a roughly 2 day period. Fiber formation was much faster than in the absence of an interface, presumably because of the close intermolecular proximity of peptides at the interfaces. While these fibers resembled protofibrils, they failed to seed the aggregation of Abeta(1-40) monomers effectively.

BRI2 (ITM2b) Inhibits A Deposition In Vivo

“…The lyophilized synthetic A␤1-42 (Mayo Clinic Peptide Synthesis Facility) was dissolved at 0.5-2.0 mM in 20 mM NaOH 15 min before size exclusion chromatography on Superdex 75 HR 10/30 column (GE Healthcare) to remove any preformed A␤ aggregates. The concentration of monomeric A␤ was determined by UV absorbance with a calculated extinction coefficient of 1450 cm Ϫ1 ϫ M Ϫ1 at 276 nm (Rangachari et al, 2006). A␤1-42 aggregation reactions were initiated in siliconized Eppendorf tubes by incubating 25-50 M freshly purified A␤1-42 monomer in 10 mM Tris-HCl and 150 mM NaCl, pH 8.0, buffer without agitation at 37°C.…”

“…A␤1-42 aggregation reactions were initiated in siliconized Eppendorf tubes by incubating 25-50 M freshly purified A␤1-42 monomer in 10 mM Tris-HCl and 150 mM NaCl, pH 8.0, buffer without agitation at 37°C. Monomeric A␤1-42 aggregation process in the presence or absence of Bri2-23 peptide were monitored using a thioflavin T (ThT) assay as previously reported (Rangachari et al, 2006). Atomic force microscopy images were obtained with a NanoScope III controller with a Multimode AFM (Veeco Instruments) as described previously (Nichols et al, 2005).…”

Inhibition of β-amyloid1-40 Peptide Aggregation and Neurotoxicity by Citrate

“…Rangachari et al found over a narrow range of SDS concentrations that SDS accelerated aggregation (Rangachari et al, 2006). Jeng et al (2006) found that SDS could inhibit fibril formation by Aβ1-40 via the formation of a small peptide/SDS complex in aqueous solutions (Jeng et al, 2006), and this inhibitory effect is enhanced by SDS micelles when a larger SDS concentration is used.…”

Aptamers

“…Besides GO, gold-based nanomaterials and derivatives have attracted considerable attention for the crafting of aptamer-based materials and devices due to their stability and their advantageous optical and electronic properties [170][171][172]. In particular, gold nanoparticles have served as drug delivery systems for aptamers since they generally increase the stability of ssDNA towards nuclease degradation, the cellular uptake capacity of oligonucleotides, as well as their biocompatibility and usually induce a limited immune response [173,174].…”

“…Besides the use of gold nanoparticles as drug delivery systems and diagnostic tools, Niu et al demonstrated that conjugation of the sgc8c aptamer [19] with a gold N-heterocyclic gold (I) complex (NHC-Au I -aptamer), known to induce cell apoptosis, resulted in internalization of the bioconjugate specifically into CCRF-CEM leukemia cells and exhibited excellent cytotoxicity [171]. The sgc8c-7aptamer employed in this strategy targeted the receptor protein tyrosine kinase 7 (PTK-7) that is overexpressed in CCRF-CEM leukemia cells and allowed for a 30-fold increase in cytotoxicity compared to the unmodified NHC-Au I complex.…”