AA amyloid fibrils from diseased tissue are structurally different from in vitro formed SAA fibrils

Systemic AA amyloidosis is a world-wide occurring protein misfolding disease of humans and animals. It arises from the formation of amyloid fibrils from serum amyloid A (SAA) protein. Using cryo electron microscopy we here show that amyloid fibrils which were purified from AA amyloidotic mice are structurally different from fibrils formed from recombinant SAA protein in vitro. Ex vivo amyloid fibrils consist of fibril proteins that contain more residues within their ordered parts and possess a higher β-sheet content than in vitro fibril proteins. They are also more resistant to proteolysis than their in vitro formed counterparts. These data suggest that pathogenic amyloid fibrils may originate from proteolytic selection, allowing specific fibril morphologies to proliferate and to cause damage to the surrounding tissue.

Recent Studies on Design and Development of Drugs Against Alzheimer’s Disease (AD) Based on Inhibition of BACE-1 and Other AD-causative Agents

Background: Alzheimer’s disease (AD) is one of the neurodegenerative diseases and has been hypothesized to be a protein misfolding disease. In the generation of AD, β-secretase, γ-secretase, and tau protein play an important role. A literature search reflects ever increasing interest in the design and development of anti-AD drugs targeting β-secretase, γ-secretase, and tau protein. Objective: The objective is to explore the structural aspects and role of β-secretase, γ-secretase, and tau protein in AD and the efforts made to exploit them for the design of effective anti-AD drugs. Methods: The manuscript covers the recent studies on design and development of anti-AD drugs exploiting amyloid and cholinergic hypotheses. Results: Based on amyloid and cholinergic hypotheses, effective anti-AD drugs have been searched out in which non-peptidic BACE1 inhibitors have been most prominent. Conclusion: Further exploitation of the structural aspects and the inhibition mechanism for β-secretase, γ-secretase, and tau protein and the use of cholinergic hypothesis may lead still more potent anti-AD drugs.

Role of domain interactions in the aggregation of full-length immunoglobulin light chains

Amyloid light-chain (LC) amyloidosis is a protein misfolding disease in which the aggregation of an overexpressed antibody LC from a clonal plasma cell leads to organ toxicity and patient death if left untreated. While the overall dimeric architecture of LC molecules is established, with each LC composed of variable (VL) and constant (CL) domains, the relative contributions of LC domain–domain interfaces and intrinsic domain stabilities to protection against LC aggregation are not well understood. To address these topics we have engineered a number of domain-destabilized LC mutants and used solution NMR spectroscopy to characterize their structural properties and intrinsic stabilities. Moreover, we used fluorescence spectroscopy to assay their aggregation propensities. Our results point to the importance of both dimerization strength and intrinsic monomer stability in stabilizing VL domains against aggregation. Notably, in all cases considered VL domains aggregate at least 10-fold faster than full-length LCs, establishing the important protective role of CL domains. A strong protective coupling is found between VL–VL and CL–CL dimer interfaces, with destabilization of one interface adversely affecting the stability of the other. Fibril formation is observed when either the VL or CL domain in the full-length protein is severely destabilized (i.e., where domain unfolding free energies are less than 2 kcal/mol). The important role of CL domains in preventing aggregation highlights the potential of the CL–CL interface as a target for the development of drugs to stabilize the dimeric LC structure and hence prevent LC amyloidosis.

Immunoglobulin light chain amyloid aggregation

Light chain (AL) amyloidosis is a devastating, complex, and incurable protein misfolding disease.