Diseases, involving amyloids

The conformational plasticity supported by mobile regions within native proteins, partially denatured protein states such as molten globules, and natively unfolded proteins underlies many of the conformational (protein misfolding) diseases (Carrell and Lomas, 1997 Dobson et al., 2001). Many of these diseases involve amyloid fibril formation, as in amyloidosis from mutant human lysozymes, neurodegenerative diseases such as Parkinson s and Alzheimer s due to the hbrillogenic propensities of a -synuclein and tau, and the prion encephalopathies such as scrapie, BSE, and new variant Creutzfeldt-Jacob disease (CJD) where amyloid fibril formation is triggered by exposure to the amyloid form of the prion protein. In addition, aggregation of serine protease inhibitors such as a j-antitrypsin is responsible for diseases such as emphysema and cirrhosis. 

Fig. 13.8. Correlation between expression levels and the measured aggregation rates for a set of human proteins. The aggregation rates represent all the data obtained from a comprehensive search of the amyloid aggregation literature, for studies carried out at pH values between 4.0 and 8.0. The expression levels are estimated from the cellular mRNA concentration and are taken from published databases. The standard deviations of the aggregation rates are reported only in four cases, as these values are generally not available or difficult to extract from the literature. Data for two proteins not involved in any known medical conditions are included in the plot while the other points correspond to proteins that are associated with amyloid diseases. From [4]...

A number of diseases involve deposition of a characteristic amyloid fiber. However, in each of these diseases, the amyloid is derived from a different protein that has changed its conformation (three-dimensional structure) to that of the amyloid repeated p-sheet structure. Once amyloid deposition begins, it seems to proceed rapidly, as if the fibril itself were promoting formation and deposition of more fibrils (a phenomenon called "seeding"). The different clinical presentations in each of these diseases results from differences in the function of the native protein and the site of amyloid deposition. 

Numerous pathogenic proteins have the capability to perturb brain functions and to trigger, maintain, or amplify brain diseases. Schematically, we can class these proteins in two main categories endogenous brain proteins with amyloid/aggregative properties (the so-called amyloid proteins involved in Alzheimer s and Parkinson s diseases) and infectious microbial proteins such as the surface envelope glycoprotein gpl20 that can either play a role in the infection process of brain cells or act as a neurotoxin. " In any case, these proteins... 

Amyloid precursor protein (APP) is the precursor of (3-amyloid, the main component of senile plaques found in the brain of Alzheimer patients. The production of (3-amyloid from APP to the cells from abnormal proteolytic cleavage of the amyloid precursor protein. Enzymes involved in this cleavage may be suitable targets for the therapy of Alzheimer s disease. 

Alzheimer s disease in which the pathogenicity of amyloid peptides depends on proteases, namely secretases, involved in amyloid precursor protein (APP) maturation. This chapter will describe how the proteolysis of chemokines might participate in the neuropathogenesis of HIV infection, thus contributing to the development of the central nervous system disorder termed HIV-associated dementia (HAD). 

Evidence for a neuroimmunological involvement in Alzheimer s disease is accumulating. Activation of the complement cascade by beta amyloid (Rogers et al., 1992), the recruitment, proliferation and activation of microglia in intimate juxtaposition to the senile plaques (Davis et al., 1992), and the increased synthesis of microglia-derived pro-inflammatory cytokine interleukin-1 (Griffin et al., 1989) is indicative of a chronic inflam-... 

BACE-1 (p-secretase) is one of the enzymes involved in breaking down APP to produce Ap (amyloid p-peptide, Ap40>42), the protein that eventually oligomerizes to form Ap plaques, the hallmark of Alzheimer s disease (AD). Thus an agent that... 

The lack of zinc can also be a problem in biological systems and is responsible for disease states. For example, nitric oxide-dependent apoptosis can be induced in motor neurons by zinc-deficient SOD, and in some cases of amyotrophic lateral sclerosis, zinc-deficient SOD may participate in this type of oxidative mechanism involving nitric oxide.969 One form of hereditary human hair loss or alopecia was mapped to a specific gene and a mutation found in affected individuals. The gene encodes a single zinc finger transcription factor protein with restricted expression in the brain and skin.970 Zinc has been implicated in Alzheimer s via beta amyloid formation, and a role has been attributed for the cerebral zinc metabolism in the neuropathogenesis of Alzheimer s disease.971... 

The failure of proteins to fold into their functional forms can occasionally lead to "misfolding" or "conformational" diseases.140 Many of these diseases are associated with the formation of amyloid protein, an insoluble material that is deposited as fibrils or plaques in different tissues and organs of the body. They include amyloid Ap protein as the major constituent of the plaques in Alzheimer patients, PrPc associated with neuro-degenerative diseases, a-synuclein (AS) associated with Parkinson s diseases, transthyretin (TTR) as a homotetrameric protein that is involved in the transport of thyroid hormones and retinol in human serum. In particular, the Ap protein is a peptide of 39-43 amino acids that is the... 

The 140-residue protein AS is able to form amyloid fibrils and as such is the main component of protein inclusions involved in Parkinson s disease. Full-length 13C/15N-labelled AS fibrils and AS reverse-labelled for two of the most abundant amino acids, K and V, were examined by homonuclear and heteronuclear 2D and 3D NMR.147 Two different types of fibrils display chemical shift differences of up to 13 ppm in the l5N dimension and up to 5 ppm for the backbone and side-chain 13C chemical shifts. Selection of regions with different mobility indicates the existence of monomers in the sample and allows the identification of mobile segments of the protein within the fibril in the presence of monomeric protein. At least 35 C-terminal residues are mobile and lack a defined secondary structure, whereas the N terminus is rigid starting from residue 22. In addition, temperature-dependent sensitivity enhancement is also noted for the AS fibrils due to both the CP efficiency and motional interference with proton decoupling.148... 

The sustained attractiveness of photolabeling is apparent from its prominence in studies of y-secretase, an intramembrane protease that contributes to forming amyloid-p peptides and is a major target in Alzheimer s disease [60-62]. y-Secretase is a complex of at least four different polypeptides, and is difficult to engage with high-resolution structural methods. However, in a case of this kind that involves a known target, immunodetection of proteins can often specify the target of y-secretase inhibitor photoaffinity probes such as 19, and proteomic mass spectrometry is not needed. 

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