Eleonora Cerasoli

Amyloid-beta (Aβ) peptide oligomers are believed to be the causative agents of Alzheimer’s disease (AD). Though post-mortem examination shows that insoluble fibrils are deposited in the brains of AD patients in the form of intracellular (tangles) and extracellular (plaques) deposits, it has been observed that cognitive impairment is linked to synaptic dysfunction in the stages of the illness well before the appearance of these mature deposits. Increasing evidence suggests that the most toxic forms of Aβ are soluble low-oligomer ligands whose amounts better correlate with the extent of cognitive loss in patients than those of fibrillar insoluble forms. Therefore, these ligands hold the key to a better understanding of AD prompting the search for clearer correlations between their structure and toxicity. The importance of such correlations and their diagnostic value for the early diagnosis of AD is discussed here with a particular emphasis on the transient nature and structural plasticity of misfolded Aβ oligomers.

Proteins are used as drugs against different pathologies because of their potential specificity of action with fewer side effects. However, their production and successful storage imposes a greater challenge compared to small molecule drugs. Though the determination of protein thermal stability is commonly used to find the optimum storage conditions for biopharmaceuticals, a multi-technique approach should be applied more often when investigating complex systems to understand the structure of the species that contribute to the different transitions, thereby gaining insight about the processes of both unfolding and aggregation. This knowledge is crucial for identifying those conformational changes which are likely to lead to aggregation/degradation allowing a more rational approach to biopharmaceutical production and formulation. This is particularly important in the case of multi-domain proteins, such as IgGs, which can undergo multiple transitions due to independent unfolding of the domains. In this work, we have followed the thermal denaturation of a monoclonal antibody by using different biophysical techniques with complementary strengths, providing an example of how the information gathered suggests a way to intervene to stabilise the wanted conformation (monomeric protein). Indeed, in this particular case, an optimisation of storage conditions based on only thermal stability studies would have led to the stabilisation of an undesired product, a population of low molecular weight oligomers.