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 (Zβ2m_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 Zβ2m_01 has the potential to act as β2m aggregation inhibitor under lysosomal-like pH values.