Solution Structure of an Amyloid-Forming Protein During Photoinitiated Hexamer−Dodecamer Transitions Revealed through Small-Angle Neutron Scattering

Abstract

Shape-reconstruction analysis applied to small angle neutron scattering (SANS) data is used to determine the in vitro conformations of alpha-chymotrypsin oligomers that form as a result of partial unfolding with a photoresponsive surfactant. In the presence of the photoactive surfactant under visible light, the native oligomers (dimers or compact hexamers) rearrange into expanded corkscrew-like hexamers. Converting the surfactant to the photopassive form with UV light illumination causes the hexamers to laterally aggregate and intertwine into dodecamers with elongated, twisted conformations containing cross-sectional dimensions similar to amyloid protofilaments. Secondary-structure measurements with FT-IR indicate that this photoinduced hexamer-to-dodecamer association occurs through intermolecular beta sheets stabilized with hydrogen bonds, similar to amyloid formation. Traditional structural characterization techniques such as X-ray crystallography and NMR are not easily amenable to the study of these non-native protein conformations; however, SANS is ideally suited to the study of these associated intermediates, providing direct observation of the mechanism of oligomeric formation in an amyloid-forming protein. Combined with photoinitiated hexamer-to-dodecamer associations in the presence of the photoresponsive surfactant, this study could provide unique insight into the amyloidosis disease pathway, as well as novel disease treatment strategies.

Inhibition of Alzheimer amyloid β aggregation by polyvalent trehalose

“…For example, polyvalent trehalose with a short alkyl chain (2) showed a strong inhibitory effect, but polyvalent trehalose with a longer alkyl chain (3) induced amyloid formation. It has been reported that amyloid formation is induced by surfactants of amphiphilic molecules [25][26][27]. Not only the saccharide structure of the polymer but also amphiphilicity plays important roles in the amyloid formation and inhibition.…”

Spatial and temporal control of surfactant systems

“…Complementary studies with trans -azoTAB have also provided evidence that trans -azoTAB can bind more strongly than cis -azoTAB to hydrophobic domains of some proteins, and lead to light-induced changes in the secondary, 46 tertiary, 5, 90 and quaternary structure 91 (i.e., degree of unfolding of proteins). For bovine serum albumin, a series of structural transitions was indentified, and addition of trans -azoTAB led to transitions between the structural states denoted as N, N d , F and E. The concentrations required for trans -azoTAB to cause the N to N d , N d to F, and F to E were 0.55mM, 0.8mM and 2.83mM, respectively.…”

“…This proposition has led to a series of recent investigations in which the interactions of azobenzene-based surfactants with DNA 32, 88, 89 or proteins 5, 46, 47, 90, 91 have been reported.…”

“…It is noteworthy, however, that the effects of azoTAB on protein conformation are different for different proteins. For α-chymotrypsin, which self-associates to form either a dimer at pH 3 or a hexamer at pH 7, 91 addition of trans -azoTAB converted the native structure (dimers or compact hexamers) into expanded corkscrew-like hexamers. It was observed that the trans -to- cis photoisomerization led to changes in the quaternary structure, with the hexamers aggregating laterally into rope-like dodecamers.…”

Reversible control of enzyme‐inhibitor interactions with light illumination using a photoresponsive surfactant

“…Under visible light, ~75% of azoTAB adopts the relatively hydrophobic trans conformation, while under UV light ~90% of the surfactant exists as the relatively hydrophilic cis isomer. This provides a means to photoreversibly control protein‐surfactant interactions, as demonstrated by our previous studies . In the case of carbonic anhydrase, for example, the protein was found to dramatically unfold and, thus, inactivate in the presence of the trans surfactant, while the unfolding was reversed to a native‐like enzyme conformation and activity upon UV illumination, resulting in enzyme reactivation .…”