Kinetic study of beta-amyloid residue accessibility using reductive alkylation and mass spectrometry

The role of integrins in brain health and neurodegenerative diseases

Integrins are heterodimeric membrane proteins expressed on the surface of most cells. They mediate adhesion and signaling processes relevant for a wealth of physiological processes, including nervous system development and function. Interestingly, integrins are also recognized therapeutic targets for inflammatory diseases, such as multiple sclerosis. Here, we discuss the role of integrins in brain development and function, as well as in neurodegenerative diseases affecting the brain (Alzheimer's disease, multiple sclerosis, stroke). Furthermore, we discuss therapeutic targeting of these adhesion receptors in inflammatory diseases of the brain.

Protein Footprinting via Covalent Protein Painting Reveals Structural Changes of the Proteome in Alzheimer's Disease

Misfolding and aggregation of amyloid-β peptide and hyperphosphorylated tau are molecular markers of Alzheimer's disease (AD), and although the 3D structures of these aberrantly folded proteins have been visualized in exquisite detail, no method has been able to survey protein folding across the proteome in AD. Here, we present covalent protein painting (CPP), a mass spectrometry-based protein footprinting approach to quantify the accessibility of lysine ε-amines for covalent modification at the surface of natively folded proteins. We used CPP to survey the reactivity of 2645 lysine residues and therewith the structural proteome of HEK293T cells and found that reactivity increased upon mild heat shock. CPP revealed that the accessibility of lysine residues for covalent modification in tubulin-β (TUBB), in succinate dehydrogenase (SHDB), and in amyloid-β peptide (Aβ) is altered in human postmortem brain samples of patients with neurodegenerative diseases. The structural alterations of TUBB and SHDB in patients with AD, dementia with Lewy bodies (DLB), or both point to broader perturbations of the 3D proteome beyond Aβ and hyperphosphorylated tau.

The catalytic kinetics of chicken transthyretin towards human Aβ1-42

The novel property of transthyretin (TTR) as a protease has been proposed to be significant. However, the study of TTR proteolysis properties has not been completely elucidated. Herein, we first report the catalytic activity of chicken TTR from plasma determined by using fluorescently labeled amyloid beta 1-42 peptide (Aβ_1-42), and compared it with human TTR (human TTR) from plasma and recombinant Crocodylus porosus TTR. The enzyme kinetic study revealed that the affinity for Aβ_1-42 of chicken TTR and C. porosus TTR (K_M values were 12.72 ± 0.27 μM and 16.21 ± 0.02 μM, respectively) were significantly lower than human TTR (K_M was 43.05 ± 0.39 μM). In addition, the catalytic efficiency of chicken TTR (K_cat/K_M was 310,386.87 ± 13,627.12 M^-1 s^-1) was 4.3 and 5.5 folds higher than those of C. porosus TTR and human TTR (K_cat/K_M were 72,893.80 ± 355.74 M^-1 s^-1 and 56,519.12 ± 5009.50 M^-1 s^-1, respectively), respectively. These results does not only indicated the relationship between structure and the proteolytic activity of TTR, but also suggested a potential development of TTR as a therapeutic anti-Aβ agent.

Beta-amyloid auto-antibodies are reduced in Alzheimer's disease

Accumulation and cytotoxicity of amyloid beta (Aβ) are understood as the major cause of Alzheimer's disease (AD). There is evidence that naturally occurring antibodies against amyloid beta (Aβ) protein play a role in Aβ-clearance, and such a mechanism appears to be impaired in AD. In the present study, the anti-Aβ antibodies in the serum from individuals with and without late onset AD were measured using ELISA and dot-blot methods. Aβ auto-antibodies in serum were mainly targeted to Aβ1-15 epitope and its titer was significantly lower in AD patients than elderly non-AD controls (NC). The dot-blot analysis further demonstrated that auto-antibodies against fibrillar Aβ42, Aβ1-15 and Aβ16-30 epitopes were all in a lower level in AD than in NC. The isotypes of the auto-antibodies were mainly non-inflammatory IgG2 type. We also analyzed the relationship of auto-Aβ antibody levels with the genotypes of apolipoprotein E (ApoE) and ANKK1/DRD2 gene.

Biochemistry of amyloid β-protein and amyloid deposits in Alzheimer disease

Progressive cerebral deposition of the amyloid β-protein (Aβ) in brain regions serving memory and cognition is an invariant and defining feature of Alzheimer disease. A highly similar but less robust process accompanies brain aging in many nondemented humans, lower primates, and some other mammals. The discovery of Aβ as the subunit of the amyloid fibrils in meningocerebral blood vessels and parenchymal plaques has led to innumerable studies of its biochemistry and potential cytotoxic properties. Here we will review the discovery of Aβ, numerous aspects of its complex biochemistry, and current attempts to understand how a range of Aβ assemblies, including soluble oligomers and insoluble fibrils, may precipitate and promote neuronal and glial alterations that underlie the development of dementia. Although the role of Aβ as a key molecular factor in the etiology of Alzheimer disease remains controversial, clinical trials of amyloid-lowering agents, reviewed elsewhere in this book, are poised to resolve the question of its pathogenic primacy.

The use of mass spectrometry to study amyloid-β peptides

Amyloid-β peptide (Aβ) varies in size from 39 to 43 amino acids and arises from sequential β- and γ-secretase processing of the amyloid precursor protein. Whereas the non-pathological role for Aβ is yet to be established, there is no disputing that Aβ is now widely regarded as central to the development of Alzheimer's disease (AD). The so named "amyloid cascade hypothesis" states that disease progression is the result of an increased Aβ burden in affected areas of the brain. To elucidate the Aβ role in AD, many analytical approaches have been proposed as suitable tools to investigate not only the total Aβ load but also many other issues that are considered crucial for AD, such as: (i) the aggregation state in which Aβ is present; (ii) its interaction with other species or metals; (iii) its ability to induce oxidative stress; and (iv) its degradative pathways. This review provides an insight into the use of mass spectrometry (MS) in the field of Aβ investigation aimed to assess its role in AD. In particular, the different MS-based approaches applied in vitro and in vivo that can provide detailed information on the above-mentioned issues are reviewed. Moreover, the advantages offered by the MS methods over all the other techniques are highlighted, together with the recent developments and uses of combined analytical approaches to detect and characterize Aβ.

Structurally distinct toxicity inhibitors bind at common loci on β-amyloid fibril

The accumulation of aggregated β-Amyloid (Aβ) in the brain is a hallmark of Alzheimer's disease and is thought to play a role in the neurotoxicity associated with the disease. The mechanism by which Aβ aggregates induce toxicity is uncertain. Nonetheless, several small molecules have been found to interact with Aβ fibrils and to prevent their toxicity. In this paper we studied the binding of these known toxicity inhibitors to Aβ fibrils, as a means to explore surfaces or loci on Aβ aggregates that may be significant in the mechanism of action of these inhibitors. We believe knowledge of these binding loci will provide insight into surfaces on the Aβ fibrils important in Aβ biological activity. The program DOCK was used to computationally dock the inhibitors to an Aβ fibril. The inhibitors docked at two shared binding loci, near Lys28 and at the C-termini near Asn27 and Val39. The docking predictions were experimentally verified using lysine specific chemical modifications and Aβ fibrils mutated at Asn27. We found that both Congo red and Myricetin, despite being structurally different, bound at the same two sites. Additionally, our data suggests that three additional Aβ toxicity inhibitors may also bind in one of the sites. Identification of these common binding loci provides targets on the Aβ fibril surface that can be tested in the future for their role in Aβ biological activity.