Affibodies as valuable tool to prevent β₂m aggregation under lysosomal-like conditions

Beta-2 microglobulin (β₂m) is a small protein that forms the invariant subunit of the Major Histocompatibility Complex I. Monomeric β₂m is stable under physiological conditions, however high local concentrations can induce misfolding, leading to amyloid deposition. This accumulation has been recently observed in the lysosomes of tumour-associated macrophages from patients affected by multiple myeloma. Such aggregation has been linked to inflammation and tumour progression. Stabilizing the native state of β₂m could be the first step towards preventing this cancer-promoting process. To achieve this goal, the effect of affibody molecules, small and stress-resistant affinity proteins, was tested. Three affibodies molecules were selected against β₂m. Affibody-β₂m complex formation was initially assessed by size exclusion chromatography and subsequently confirmed by microscale thermophoresis and isothermal titration calorimetry. In parallel, in presence of one of the affibody (Z_{β2m_01}) a significant reduction in β₂m aggregation was observed. The inhibition of amyloid formation was also confirmed by transmission electron microscopy. Taken together, these results indicate that Z_{β2m_01} has the potential to act as β₂m aggregation inhibitor under lysosomal-like pH values.