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Protein conformational diseases, including Alzheimer's, Huntington's, and Parkinson's diseases, result from protein misfolding, giving a distinct fibrillar feature termed amyloid. Recent studies show that only the globular (not fibrillar) conformation of amyloid proteins is sufficient to induce cellular pathophysiology. However, the 3D structural conformations of these globular structures, a key missing link in designing effective prevention and treatment, remain undefined as of yet. By using atomic force microscopy, circular dichroism, gel electrophoresis, and electrophysiological recordings, we show here that an array of amyloid molecules, including amyloid-[beta](1-40), [alpha]-synuclein, ABri, ADan, serum amyloid A, and amylin undergo supramolecular conformational change. In reconstituted membranes, they form morphologically compatible ion-channel-like structures and elicit single ion-channel currents. These ion channels would destabilize cellular ionic homeostasis and hence induce cell pathophysiology and degeneration in amyloid diseases. atomic force microscopy | protein conformational disease | peptide ion channel | misfolding protein | 3D structure

Haemophilus influenzae is one of five bacterial species known to produce IgA proteases, enzymes that specifically cleave the human IgA1 heavy chain. Strains of H. influenzae produce three distinct types of IgA proteases that cleave different peptide bonds within the IgA1 hinge region. Type 1 protease cleaves the prolyl-seryl bond at position 231–232; type 2 protease cleaves the prolyl-threonyl bond at position 235–236, the same bond attacked by Neisseria gonorrhoeae and Neisseria meningitidis type 2 proteases. Type 3 protease yields a unique double Fd cleavage pattern; the exact peptide bonds cleaved have not been determined. The type of protease produced correlates with the serotype, but not with the biotype, of the isolate; serotypes A, B, D, and F produce primarily type 1 protease, whereas serotypes C and E produce only type 2 enzyme. Each nontypable strain yields one of the three protease types. These data further extend our knowledge of the extreme specificity of the IgA proteases and suggest that IgA protease type may be useful in the taxonomy and epidemiology of H. influenzae. [ABSTRACT FROM PUBLISHER]

Transmembrane proteins BRI2 and amyloid precursor protein (APP) co-localize with amyloid β (Aβ) lesions in sporadic Alzheimer disease and mutations in both precursor proteins are linked to early-onset familial cases of cerebral amyloidosis associated with dementia and/or cerebral hemorrhage. A specific interaction between BRI2 and APP was unveiled by immunoprecipitation experiments using transfected and non-transfected cells. The use of deletion mutants further revealed that stretches 648–719 of APP751 and 46–106 of BRI2, both inclusive of the full transmembrane domains, are sufficient for the interaction. Removal of most of the APP and BRI2 extracellular domains without affecting the interaction implies that both proteins interact when are expressed on the same cell membrane (cis) rather than on adjacent cells (trans). The presence of BRI2 had a modulatory effect on APP processing, specifically increasing the levels of cellular APP as well as β-secretase-generated COOH-terminal fragments while decreasing the levels of a-secretase-generated COOH-terminal fragments as well as the secretion of total APP and Aβ peptides. Determining the precise molecular pathways affected by the specific binding between APP and BRI2 could result in the identification of common therapeutic targets for these sporadic and familial neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

To better understand the physiologic excretion and/or catabolism of circulating peripheral amyloid β (Aβ), we labeled human Aβ40 (monomeric, with predominant unordered structure) and Aβ42 (mixture of monomers and oligomers in ∼50:50 ratio, rich in β-sheet conformation) with either Na125I or 125I-tyramine cellobiose, also known as the cell-trapping ligand procedure, testing their blood clearance and organ uptake in B6SJLF1/J mice. Irrespective of the labeling protocol, the peptide conformation, and the degree of oligomerization, both Aβ40 and Aβ42 showed a short half-life of 2.5-3.0 min. The liver was the major organ responsible for plasma clearance, accounting for >60% of the peptide uptake, followed by the kidney. In vivo, hepatocytes captured >90% of the radiolabeled peptides which, after endocytosis, were preferentially catabolized and excreted into the bile. Biliary excretion of intact as well as partially degraded AB species became obviously relevant at doses above 10 µg. The use of biotin-labeled Aβ allowed the visualization of the interaction with HepG2 cells in culture, whereas competitive inhibition experiments with unlabeled Aβ demonstrated the specificity of the binding. The capability of the liver to uptake, catabolize, and excrete large doses of Aβ, several orders of magnitude above its physiologic concentration, may explain not only the femtomolar plasma levels of AB but the little fluctuation observed with age and disease stages. [ABSTRACT FROM AUTHOR]