Exploring critical determinants of protein amyloidogenesis: a review

Imidazolium-based ionic liquids with increasing alkyl chain length of cations decrease the stability and fibrillation propensity of lysozyme

Imidazolium ionic liquids with longer alkyl side chains show a larger destabilization effect on lysozyme. Increased hydrophobicity of the IL increases its binding affinity and inhibits the fibril formation of lysozyme.

Interaction of selected biomolecules and metabolites with amyloidogenic proteins

The current manuscript reports docking and molecular interaction analyses of three FDA approved acetylcholinesterase inhibitors, nitrogenous bases and nucleotides with amyloidogenic proteins like hen egg white lysozyme (HEWL) and amyloid β peptide. After prediction of aggregation-prone regions in hen egg-white lysozyme and amyloid β peptide, grid boxes were defined for docking purposes covering these regions. We analyzed vital interactions and binding modes of molecules that dock near aggregation-prone regions of these proteins with acceptable statistics. The data hints toward the possibility that these molecules may bind to aggregation-prone regions and prevent amyloid/aggregation formation. We have also compared the binding energy and interactions of these molecules with certain other natural molecules viz. Curcumin, Coumarin and Resveratrol that have been previously reported to show anti-amyloidogenic activity as positive controls.Communicated by Ramaswamy H. Sarma.

Gold nanoparticles partition to and increase the activity of glucose-6-phosphatase in a synthetic phospholipid membrane system

Engineered nanomaterials can alter the structure and/or function of biological membranes and membrane proteins but the underlying mechanisms remain unclear. We addressed this using a Langmuir phospholipid monolayer containing an active transmembrane protein, glucose-6-phosphatase (G6Pase). Gold nanoparticles (nAu) with varying ligand shell composition and hydrophobicity were synthesized, and their partitioning in the membrane and effects on protein activity characterized. nAu incorporation did not alter the macroscopic properties of the membrane. Atomic force microscopy showed that when co-spread with other components prior to membrane compression, nAu preferentially interacted with G6Pase and each other in a functional group-dependent manner. Under these conditions, all nAu formulations reduced G6Pase aggregation in the membrane, enhancing catalytic activity 5-6 fold. When injected into the subphase beneath pre-compressed monolayers, nAu did not affect G6Pase activity over 60 minutes, implying they were unable to interact with the protein under these conditions. A small but significant quenching of tryptophan fluorescence showed that nAu interacted with G6Pase in aqueous suspension. nAu also significantly reduced the hydrodynamic diameter of G6Pase in aqueous suspension and promoted catalytic activity, likely via a similar mechanism to that observed in co-spread monolayers. Overall, our results show that nAu can incorporate into membranes and associate preferentially with membrane proteins under certain conditions and that partitioning is dependent upon ligand shell chemistry and composition. Once incorporated, nAu can alter the distribution of membrane proteins and indirectly affect their function by improving active site accessibility, or potentially by changing their native structure and distribution in the membrane.

Concentration dependent switch in the kinetic pathway of lysozyme fibrillation: Spectroscopic and microscopic analysis

Formation of amyloid fibrils is found to be a general tendency of many proteins. Investigating the kinetic mechanisms and structural features of the intermediates and the final fibrillar state is essential to understand their role in amyloid diseases. Lysozyme, a notable model protein for amyloidogenic studies, readily formed fibrils in vitro at neutral pH in the presence of urea. It, however, showed two different kinetic pathways under varying urea concentrations when probed with thioflavin T (ThT) fluorescence. In 2M urea, lysozyme followed a nucleation-dependent fibril formation pathway which was not altered by varying the protein concentration from 2mg/ml to 8mg/ml. In 4M urea, the protein exhibited concentration dependent change in the mechanism. At lower protein concentrations, lysozyme formed fibrils without any detectable nuclei (nucleation-independent polymerization pathway). When the concentration of the protein was increased above 3mg/ml, the protein followed nucleation-dependent polymerization pathway as observed in the case of 2M urea condition. This was further verified using microscopic images of the fibrils. The kinetic parameters such as lag time, elongation rate, and fibrillation half-time, which were derived from ThT fluorescence changes, showed linear dependency against the initial protein concentration suggested that under the nucleation-dependent pathway conditions, the protein followed primary-nucleation mechanism without any significant secondary nucleation events. The results also suggested that the differences in the initial protein conformation might alter the mechanism of fibrillation; however, at the higher protein concentrations lysozyme shifted to nucleation-dependent pathway.

Amyloid associated with neoplasia in two captive tricolour sharkminnows Balantiocheilus melanopterus Bleeker

Amyloid associated with pancreatic adenocarcinoma was discovered in two captive adult tricolour sharkminnows Balantiocheilus melanopterus Bleeker found dead in a freshwater display. Enlarged abdomens expanded by bloody ascitic fluid and grossly visible masses of abnormal tissue were present surrounding sections of the stomach and intestine. Histologically, the masses were composed of areas of well-organized exocrine pancreatic acini interspersed with cords of poorly differentiated, spindle-shaped cells that compressed and effaced normal parenchyma. These cells possessed small numbers of cytoplasmic zymogen granules; the exocrine nature of these cells was confirmed using transmission electron microscopy (TEM). Fibrovascular connective tissue of the hepatopancreas and mesenteries was expanded by lightly eosinophilic, hyaline, homogeneous acellular material. Similar material greatly expanded the tunica media of large blood vessels in the hepatopancreas. After staining with Congo red or thioflavin T, this material exhibited red-green dichroism under polarized light or bright green fluorescence under ultraviolet light (255 nm), respectively. The non-branching fibrils, of indeterminate length, had an approximate diameter of 10-20 nm using TEM. Although exocrine pancreatic neoplasia is relatively common in fish, the presence of amyloid is not. To our current knowledge, the latter has not yet been described in association with a neoplastic lesion in fish.

Minimally invasive minor salivary gland biopsy for the diagnosis of amyloidosis in a rheumatology clinic

Background. Systemic amyloidosis is a potentially fatal condition, unless diagnosed and treated before development of irreversible organ damage. Demonstration of amyloid deposits within tissue biopsies is only definitive diagnostic method, which makes appropriate selection of biopsy site essential. Herein, we evaluated efficacy of minimally invasive minor salivary gland biopsy (MSGB) for the diagnosis of amyloidosis. Methods. We analyzed 37 biopsies taken from 35 patients. Suggestive findings for amyloidosis were significant proteinuria, renal impairment, refractory diarrhea, neuropathy, and restrictive cardiomyopathy. Minor salivary gland was the initial biopsy site in all subjects. When MSGB was negative but there was a high suspicion for amyloidosis, a kidney, duodenum, or rectal biopsy was performed for further investigation. Results. Mean age of patients was 45.4 and 21 were female. In 11 patients amyloidosis was diagnosed with MSGB. In overall 18 patients were diagnosed with amyloidosis. Sixteen of them were identified as being of AA type and two were AL type amyloidosis. The sensitivity of minimally invasive MSGB is 61.1% for diagnosing amyloidosis in this study. Conclusion. MSGB is a safe and simple method for the diagnosis of amyloidosis which can be performed in an outpatient setting. We suggest extensive use of this minimally invasive method.