Spectrin's chimeric E2/E3 enzymatic activity.

In this minireview, we cover the discovery of the human erythrocyte α spectrin E2/E3 ubiquitin conjugating/ligating enzymatic activity and the specific cysteines involved. We then discuss the consequences when this activity is partially inhibited in sickle cell disease and the possibility that the same attenuation is occurring in multiple organ dysfunction syndrome. We finish by discussing the reasons for believing that nonerythroid α spectrin isoforms (I and II) also have this activity and the importance of testing this hypothesis. If correct, this would suggest that the nonerythroid spectrin isoforms play a major role in protein ubiquitination in all cell types. This would open new fields in experimental biology focused on uncovering the impact that this enzymatic activity has upon protein-protein interactions, protein turnover, cellular signaling, and many other functions impacted by spectrin, including DNA repair.

Probing and trapping a sensitive conformation: amyloid-ß fibrils, oligomers, and dimers.

Alzheimer's disease (AD) is a devastating neurodegenerative disease with pathological misfolding of amyloid-ß protein (Aß). The recent interest in Aß misfolding intermediates necessitates development of novel detection methods and ability to trap these intermediates. We speculated that two regions of Aß may allow for detection of specific Aß species: the N-terminal and 22-35, both likely important in oligomer interaction and formation. We determined via epitomics, proteomic assays, and electron microscopy that the Aß(42) species (wild type, ΔE22, and MetOx) predominantly formed fibrils, oligomers, or dimers, respectively. The 2H4 antibody to the N-terminal of Aß, in the presence of 2% SDS, primarily detected fibrils, and an antibody to the 22-35 region detected low molecular weight Aß species. Simulated molecular modeling provided insight into these SDS-induced structural changes. We next determined if these methods could be used to screen anti-Aß drugs as well as identify compounds that trap Aß in various conformations. Immunoblot assays determined that taurine, homotaurine (Tramiprosate), myoinositol, methylene blue, and curcumin did not prevent Aß aggregation. However, calmidazolium chloride trapped Aß at oligomers, and berberine reduced oligomer formation. Finally, pretreatment of AD brain tissues with SDS enhanced 2H4 antibody immunostaining of fibrillar Aß. Thus we identified and characterized Aßs that adopt specific predominant conformations (modified Aß or via interactions with compounds), developed a novel assay for aggregated Aß, and applied it to drug screening and immunohistochemistry. In summary, our novel approach facilitates drug screening, increases the probability of success of antibody therapeutics, and improves antibody-based detection and identification of different conformations of Aß.

Amyloid-ß metabolite sensing: biochemical linking of glycation modification and misfolding.

Glycation is the reaction of a reducing sugar with proteins and lipids, resulting in myriads of glycation products, protein modifications, cross-linking, and oxidative stress. Glycation reactions are also elevated during metabolic dysfunction such as in Alzheimer's disease (AD) and Down's syndrome. These reactions increase the misfolding of the proteins such as tau and amyloid-ß (Aß), and colocalize with amyloid plaques in AD. Thus, glycation links metabolic dysfunction and AD and may have a causal role in AD. We have characterized the reaction of Aß with reactive metabolites that are elevated during metabolic dysfunction. One metabolite, glyceraldehyde-3-phosphate, is a normal product of glycolysis, while the others are associated with pathology. Our data demonstrates that lipid oxidation products malondialdehyde, hydroxynonenal, and glycation metabolites (methylglyoxal, glyceraldehyde, and glyceraldehyde-3-phosphate) modify Aß42 and increase misfolding. Using mass spectrometry, modifications primarily occurred at the amino terminus. However, the metabolite methylglyoxal modified Arg5 in the Aß sequence. 4-Hydroxy-2-nonenal modifications were similar to our previous publication. To place such modifications into an in vivo context, we stained AD brain tissue for endproducts of glycation, or advanced glycation endproducts (AGE). Similar to previous findings, AGE colocalized with amyloid plaques. In summary, we demonstrate the glycation of Aß and plaques by metabolic compounds. Thus, glycation potentially links metabolic dysfunction and Aß misfolding in AD, and may contribute to the AD pathogenesis. This association can further be expanded to raise the tantalizing concept that such Aß modification and misfolding can function as a sensor of metabolic dysfunction.

Amyloids as Sensors and Protectors (ASAP) hypothesis.

This paper propounds the Amyloids as Sensors and Protectors (ASAP) hypothesis. In this novel hypothesis, we provide evidence that amyloids are capable of sensing dysfunction, and after misfolding, initiate protective cellular responses. Amyloid proteins are initially protective, but chronic stress and overstimulation of the amyloid sensor leads to pathology. This proposed ASAP hypothesis has two sequential stages: (i) sensing, and then (ii) protection. Sensing involves a conformational change of amyloids in response to the cellular environment. The protection aspect translates conformational change into a cellular response via several mechanisms. The most obvious mechanism is that protein misfolding triggers the protective unfolded protein response, and thus downregulates protein translation and increases chaperone proteins. Other documented responses include metabolic pathways and microRNAs. This ASAP hypothesis has precedence, as amyloid sensors exist (evidenced by CPEB and Sup35), and both prion and amyloid-ß sensing redox stress and metals. Our hypothesis expands on previous observations to link sensing with inciting protective cellular response. Furthermore, we substantiate the ASAP hypothesis with previously published evidence from several amyloid diseases. This novel hypothesis links disparate findings in amyloid diseases: metabolic dysfunction, unfolding protein response/chaperones, modification of amyloids, and nutrient or caloric sensing. While this hypothesis can be applied to Alzheimer's disease, it goes beyond the Alzheimer's context. Thus all amyloid proteins can potentially act as sensors of misfolding-causing stress. Finally, this hypothesis will allow for the sensor mechanism and metabolic dysfunction to serve as biomarkers of the diseases as well as therapeutic targets early in disease pathology.