Comparing the copper binding features of alpha and beta synucleins.

Amyloid aggregation of α-synuclein (AS) is one of the hallmarks of Parkinson's disease (PD). Copper ions specifically bind at the N-terminus of AS, accelerating protein aggregation. Its protein homolog ß-synuclein (BS) is also a copper binding protein, but it inhibits AS aggregation. Here, a comparative spectroscopic study of the Cu2+ binding properties of AS and BS has been performed, using electronic absorption, circular dichroism (CD) and electronic paramagnetic resonance (EPR). Our comparative spectroscopic study reveals striking similarities between the Cu2+ binding features of the two proteins. The Cu2+ binding site at the N-terminal group of BS protein, modeled by the BS (1-15) fragment is identical to that of AS; however, its rate of reduction is three times faster as compared to the AS site, consistent with BS having an additional Met residue in its Met1-Xn-Met5-Xn-Met10 motif. The latter is also evident in the cyclic voltammetry studies of the Cu-BS complex. On the other hand, the Cu2+ binding features of the His site in both proteins, as modeled by AS(45-55) and BS(60-70), are identical, indicating that the shift in the His position does not affect its coordination features. Finally, replacement of Glu46 by Ala does not alter Cu2+ binding to the His site, suggesting that the familial PD E46K mutation would not impact copper-induced aggregation. While further studies of the redox activity of copper bound to His50 in AS are required to understand the role of this site in metal-mediated aggregation, our study contributes to a better understanding of the bioinorganic chemistry of PD.

A Multicompany Assessment of Submicron Particle Levels by NTA and RMM in a Wide Range of Late-Phase Clinical and Commercial Biotechnology-Derived Protein Products.

One of the major product quality challenges for injectable biologics is controlling the amount of protein aggregates and particles present in the final drug product. This article focuses on particles in the submicron range (<2 µm). A cross-industry collaboration was undertaken to address some of the analytical gaps in measuring submicron particles (SMPs), developing best practices, and surveying the concentration of these particles present in 52 unique clinical and commercial protein therapeutics covering 62 dosage forms. Measured particle concentrations spanned a range of 4 orders of magnitude for nanoparticle tracking analysis and 3 orders of magnitude for resonant mass measurement. The particle concentrations determined by the 2 techniques differed significantly for both control and actual product. In addition, results suggest that these techniques exhibit higher variability compared to well-established subvisible particle characterization techniques (e.g., flow-imaging or light obscuration). Therefore, in their current states, nanoparticle tracking analysis and resonant mass measurement-based techniques can be used during product and process characterization, contributing information on the nature and propensity for formation of submicron particles and what is normal for the product, but may not be suitable for release or quality control testing. Evaluating the level of SMPs to which humans have been routinely exposed during the administration of several commercial and late-phase clinical products adds critical knowledge to our understanding of SMP levels that may be considered acceptable from a safety point of view. This article also discusses dependence of submicron particle size and concentration on the dosage form attributes such as physical state, primary packaging, dose strength, etc. To the best of our knowledge, this is the largest study ever conducted to characterize SMPs in late-phase and commercial products.