Transthyretin as both a Sensor and a Scavenger of β-Amyloid Oligomers

Abstract

Transthyretin (TTR) is a homotetrameric transport protein, assembled from monomers that each contains two four-stranded β-sheets and a short α-helix and loop. In the tetramer, the ‘inner’ β-sheet forms a hydrophobic pocket while the helix and loop are solvent-exposed. Beta-amyloid (Aβ) aggregates bind to TTR, and the binding is significantly reduced in mutants L82A (on the loop) and L110A (on the inner β-sheet). Protection against Aβ toxicity was demonstrated for wild-type TTR but not L82A or L110A, providing a direct link between TTR-Aβ binding, and TTR-mediated cytoprotection. Protection is afforded at substoichiometric (1:100) TTR:Aβ molar ratios, and binding of Aβ to TTR is highest for partially aggregated materials and decreased for freshly-prepared or heavily aggregated Aβ, suggesting that TTR binds selectively to soluble toxic Aβ aggregates. A novel technique, nanoparticle tracking, is used to show that TTR arrests Aβ aggregation by both preventing formation of new aggregates and inhibiting growth of existing aggregates. TTR tetramers are normally quite stable; tetrameric structure is necessary for the protein’s transport functions, and mutations that decrease tetramer stability have been linked to TTR amyloid diseases. However, TTR monomers bind more Aβ than do tetramers, presumably because the hydrophobic ‘inner’ sheet is solvent-exposed upon tetramer disassembly. Wild-type and L110A tetramers, but not L82A, were destabilized when co-incubated with Aβ, suggesting that Aβ binding to L82 triggers tetramer dissociation. Taken together, these results suggest a novel mechanism of action for TTR: the EF helix/loop ‘senses’ the presence of soluble toxic Aβ oligomers, triggering destabilization of TTR tetramers and exposure of the hydrophobic inner sheet, which then ‘scavenges’ these toxic oligomers and prevents them from causing cell death

Learning To Fold Proteins Using Energy Landscape Theory

“…Structure prediction algorithms thus can give inspiration to new studies of the misfolding kinetics. The specificity of the Velcro self-recognizing segments and the local structural uniqueness of the oligomers also give us hope for druggability of these misfolded structures with other peptides [106, 123] or small molecules.…”

A Cyclic Peptide Mimic of the β-Amyloid Binding Domain on Transthyretin

“…17 Aβ alone (28 µM) or with CG3 (2.8 µM) were prepared in PBSA and incubated for 5 h at 37 °C. Three 60 s videos were taken for each sample.…”

“…19 Briefly, primary cortical neuronal cells were cultured from embryonic15.5 day mice and were maintained in neurobasal media until they matured as previously described. 17 Aβ(1–42) (American Peptide, Sunnyvale, CA) at 1 mg/mL in PBS was diluted to 10 µM without or with peptides as previously described. 19 At 6 days in vitro (DIV), the cells were treated with either Aβ alone or Aβ incubated with different doses of mTTR and peptides.…”

TANGO-Inspired Design of Anti-Amyloid Cyclic Peptides

“…Specifically, transthyretin (TTR), a stable homotetrameric transport protein circulating in blood and cerebrospinal fluid, has been shown to be neuroprotective against A β toxicity in vitro and in AD mouse models. 29,30 Inhibition of toxicity is directly linked to TTR binding to A β ; importantly TTR preferentially binds to A β oligomers compared to fibrils, but binds only weakly to monomers. 30–32 TTR, as well as a monomeric mutant (mTTR, F87M/L110M), completely inhibits A β toxicity at substoichiometric (1:100 TTR:A β ) molar ratio.…”