Studies of proteins' formation of amyloid fibrils have revealed that potentially cytotoxic oligomers frequently accumulate during fibril formation. An important question in the context of mechanistic studies of this process is whether or not oligomers are intermediates in the process of amyloid fibril formation, either as precursors of fibrils or as species involved in the fibril elongation process or instead if they are associated with an aggregation process that is distinct from that generating mature fibrils. Here we describe and characterize in detail two well-defined oligomeric species formed by the protein α-synuclein (αSN), whose aggregation is strongly implicated in the development of Parkinson's disease (PD). The two types of oligomers are both formed under conditions where amyloid fibril formation is observed but differ in molecular weight by an order of magnitude. Both possess a degree of β-sheet structure that is intermediate between that of the disordered monomer and the fully structured amyloid fibrils, and both have the capacity to permeabilize vesicles in vitro. The smaller oligomers, estimated to contain ∼30 monomers, are more numerous under the conditions used here than the larger ones, and small-angle X-ray scattering data suggest that they are ellipsoidal with a high degree of flexibility at the interface with solvent. This oligomer population is unable to elongate fibrils and indeed results in an inhibition of the kinetics of amyloid formation in a concentration-dependent manner.

Background: Protein oligomers are implicated as cytotoxic membrane-disrupting agents in neurodegenerative diseases. Results: The small molecule EGCG, which inhibits ␣-synuclein oligomer toxicity, moderately reduces membrane binding and immobilizing the oligomer C-terminal tail. Conclusion:The ␣-synuclein oligomer may disrupt membranes by vesicle destabilization rather than pore formation. Significance: Limited reduction of oligomer membrane affinity may be sufficient to prevent cytotoxicity.

a b s t r a c tThe intrinsically disordered protein a-synuclein (aSN) is linked to Parkinson's Disease and forms both oligomeric species and amyloid fibrils. The N-terminal part of monomeric aSN interacts strongly with membranes and aSN cytotoxicity has been attributed to oligomers' ability to interact with and perturb membranes. We show that membrane folding of monomeric wt aSN and N-terminally truncated variants correlates with membrane permeabilization. Further, the first 11 N-terminal residues are crucial for monomers' and oligomers' interactions with and permeabilization of membranes. We attribute oligomer permeabilization both to cooperative electrostatic interactions through the N-terminus and interactions mediated by hydrophobic regions in the oligomer.

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Despite major advances in antibody discovery technologies, the successful development of monoclonal antibodies (mAbs) into effective therapeutic and diagnostic agents can often be impeded by developability liabilities, such as poor expression, low solubility, high viscosity and aggregation. Therefore, strategies to predict at the early phases of antibody development the risk of late-stage failure of antibody candidates are highly valuable. In this work, we employ the in silico solubility predictor CamSol to design a library of 17 variants of a humanized mAb predicted to span a broad range of solubility values, and we examine their developability potential with a battery of commonly used in vitro and in silico assays. Our results demonstrate the ability of CamSol to rationally enhance mAb developability, and provide a quantitative comparison of in vitro developability measurements with each other and with more resource-intensive solubility measurements, as well as with in silico predictors that offer a potentially faster and cheaper alternative. We observed a strong correlation between predicted and experimentally determined solubility values, as well as with measurements obtained using a panel of in vitro developability assays that probe non-specific interactions. These results indicate that computational methods have the potential to reduce or eliminate the need of carrying out laborious in vitro quality controls for large numbers of lead candidates. Overall, our study provides support to the emerging view that the implementation of in silico tools in antibody discovery campaigns can ensure rapid and early selection of antibodies with optimal developability potential.