The conversion of proteins from a soluble into a fibrillar state is associated with a wide range of pathological conditions, including neurodegenerative diseases and systemic amyloidoses. The most prominent examples are Alzheimer's, Parkinson's and the prion diseases. However, also Diabetes type 2 is associated with the deposition of a hormone, hIAPP, in the pancreas of a diabetic patient. Amyloids are defined by the ability to bind to small molecules such as Thioflavin T or Congo Red. Their structures are characterized by a high degree of beta-sheet content. In the past years, it turned out that these aggregates have a tertiary structure and adopt a well defined "fold". However, it is still unclear how large the conformtional variations are and how this conformation affects cellular toxicity.
Structural Characterization of beta-amyloid peptides (Abeta)
Alzheimer's disease is the most common form of age-related neurodegenerative disorder. Abeta is obtained after processing of APP, the amyloid precursor protein. We study Abeta fibrils using solid-state NMR in order to better understand the mechanisms which lead to the formation of these aggregates.
Abeta fibril structure
In the past few years, several structural models of Alzheimer's disease Abeta fibrils have been published (Petkova and Tycko, 2006; Paravastu and Tycko, 2008; Xiao and Ishii, 2015; Colvin and Griffin, 2016; Wälti and Riek, 2016). In these structural models, the basic fibril building block is composed of symmetric oligomers. In agreement with cryo-electron microscopy studies, we found that Abeta polymorphs can as well consist of asymmetric oligomers (Lopez del Amo et al., Angewandte Chemie 2012). We are currently working on the structural analysis of this particular amyloid polymorph. [image: Lopez del Amo et al., Angewandte Chemie 2012]
Non-steroidal anti-inflammatory drugs (NSAIDs) are known gamma-secretase modulators; they influence Abeta populations. NSAIDs are pleiotrophic and can interact with more than one pathomechanism. We demonstrated that the NSAID sulindac sulfide interacts specifically with Alzheimer disease Abeta fibrils. Sulindac sulfide does not induce drastic architectural changes in the fibrillar structure, but intercalates between the two beta-strands of the amyloid fibril and binds to hydrophobic cavities, which are found consistently in all analyzed structures (Prade et al., JBC 2015; Prade et al., Biochemistry 2016). Using chemical shift perturbation and 19F-13C distance restraints from REDOR experiments, we determine the binding site of these small molecules. The obtained results will allow to design more potent molecules for the treatment of the disease in the future. [image: Prade et al., JBC 2015]
Interactions between Small heat shock proteins and misfolding proteins
Small heat-shock proteins, including αB-crystallin (αB), play an important part in protein homeostasis, because their ATP-independent chaperone activity inhibits uncontrolled protein aggregation. Mechanistic details of human αB, particularly in its client-bound state, have been elusive, in part due to the high molecular weight and the heterogeneity of these complexes. We have shown using NMR spectroscopy, that the αB complex is assembled from asymmetric building blocks. Interaction studies demonstrated that the fibril-forming Alzheimer's disease Aβ1–40 peptide preferentially binds to a hydrophobic edge of the central β-sandwich of αB. In contrast, the amorphously aggregating client lysozyme is captured by the partially disordered N-terminal domain of αB. We suggest that αB uses its inherent structural plasticity to expose distinct binding interfaces and thus interact with a wide range of structurally variable clients (Mainz et al., Nature Struct. Mol. Biol. 2015). [image: Mainz et al., Nature Struct. Mol. Biol. 2015]