Aß42 pentamers/hexamers are the smallest detectable oligomers in solution.

Amyloid ß (Aß) oligomers may play a decisive role in Alzheimer's disease related neurodegeneration, but their structural properties are poorly understood. In this report, sedimentation velocity centrifugation, small angle neutron scattering (SANS) and molecular modelling were used to identify the small oligomeric species formed by the 42 amino acid residue long isoform of Aß (Aß42) in solution, characterized by a sedimentation coefficient of 2.56 S, and a radius of gyration between 2 and 4 nm. The measured sedimentation coefficient is in close agreement with the sedimentation coefficient calculated for Aß42 hexamers using MD simulations at µM concentration. To the best of our knowledge this is the first report detailing the Aß42 oligomeric species by SANS measurements. Our results demonstrate that the smallest detectable species in solution are penta- to hexamers. No evidences for the presence of dimers, trimers or tetramers were found, although the existence of those Aß42 oligomers at measurable quantities had been reported frequently.

Fluorescence correlation spectroscopy reveals a cooperative unfolding of monomeric amyloid-ß 42 with a low Gibbs free energy.

The amyloid-beta peptide (Aß) plays a major role in the progression of Alzheimer's disease. Due to its high toxicity, the 42 amino acid long isoform Aß42 has become of considerable interest. The Aß42 monomer is prone to aggregation down to the nanomolar range which makes conventional structural methods such as NMR or X-ray crystallography infeasible. Conformational information, however, will be helpful to understand the different aggregation pathways reported in the literature and will allow to identify potential conditions that favour aggregation-incompetent conformations. In this study, we applied fluorescence correlation spectroscopy (FCS) to investigate the unfolding of Alexa Fluor 488 labelled monomeric Aß42 using guanidine hydrochloride as a denaturant. We show that our Aß42 pre-treatment and the low-nanomolar concentrations, typically used for FCS measurements, strongly favour the presence of monomers. Our results reveal that there is an unfolding/folding behaviour of monomeric Aß42. The existence of a cooperative unfolding curve suggests the presence of structural elements with a Gibbs free energy of unfolding of about 2.8 kcal/mol.

The off-rate of monomers dissociating from amyloid-ß protofibrils.

The interconversion of monomers, oligomers, and amyloid fibrils of the amyloid-ß peptide (Aß) has been implicated in the pathogenesis of Alzheimer disease. The determination of the kinetics of the individual association and dissociation reactions is hampered by the fact that forward and reverse reactions to/from different aggregation states occur simultaneously. Here, we report the kinetics of dissociation of Aß monomers from protofibrils, prefibrillar high molecular weight oligomers previously shown to possess pronounced neurotoxicity. An engineered binding protein sequestering specifically monomeric Aß was employed to follow protofibril dissociation by tryptophan fluorescence, precluding confounding effects of reverse or competing reactions. Aß protofibril dissociation into monomers follows exponential decay kinetics with a time constant of ∼2 h at 25 °C and an activation energy of 80 kJ/mol, values typical for high affinity biomolecular interactions. This study demonstrates the high kinetic stability of Aß protofibrils toward dissociation into monomers and supports the delineation of the Aß folding and assembly energy landscape.

Antiquarian books as source of environment historical water data.

Historical environment considerations are inevitable also for modern environmental analysis. They alone allow evaluation of anthropogenic impact into the environment. To receive information about the historical environment situation in inhabited regions, we approached this task by examining historical well dated and locatable products of the Homo faber. The work introduced here uses books as a source of environment historical data specially for the environmental compartment of water. The paper of historical books, dated by their printing and allocated by their watermark(1) (Wasserzeichensammlung Piccard, Piccard online, Hauptstaatsarchiv Stuttgart, ) is a trap for traces of heavy metals contaminating their production water in historical times. Great amounts of water were brought into contact with the paper pulp in the historical paper mill process. The cellulose of the pulp acts as an ion exchange material for heavy metals, forming a dynamic equilibrium. A well defined pulp production process, starting with used clothes, allows estimation of the concentration of historical heavy metals (Cu(2+), Pb(2+), Zn(2+), Cd(2+)) in the production water (river water). Ancient papers from well dated books are eluted without destruction of their paper and the resulting solution is analysed by ETAAS and inverse stripping voltammetry to determine the historical impact of metals. Afterwards in a flow system the eluted paper spot is equilibrated with different concentrations of heavy metals (Cu(2+), Pb(2+), Zn(2+), Cd(2+)) to plot the adsorption isotherm of that very spot. Both data together allows a calculation of the heavy metal content of the historical river. For different waters of Germany and the Netherlands of the 16th-18th Century the heavy metal load could be estimated. The resulting concentrations were mostly similar to the level of modern surface waters, but in the case of the Dutch waters of the 17th Century, they were e.g. for Pb(2+) significantly higher than modern values.