Submolecular Resolution of β‑Sheet Plasticity: Decoding Mutations and PTMs in Protein Aggregation Disorders

The functional diversity of proteins often arises from the remodeling of conformational ensembles, particularly through mutations and post-translational modifications (PTMs). However, experimentally characterizing such ensembles remains challenging due to their heterogeneous and transient nature. Here, we report the determination of the conformational substates of β-sheets and the effect associated with mutations and PTMs in human islet amyloid polypeptide (hIAPP) via scanning tunneling microscopy (STM). Thanks to the ultrahigh resolution of STM, the β-sheets formed by the assembly of hIAPP were revealed to be conformationally diverse, including 17 types of conformational substates concomitant with 60 types of interconformation interactions. These conformational substates are highly heterogeneous in the folding structures but close in energy. Four mutations and PTMs were carried out with hIAPP to investigate the evolvability of the β-sheet assembly. Regulation effects accomplished by the mutations and PTMs on the conformational ensembles of β-sheets have been identified, including the number of conformational substates, the most probable substates, and the topography of the energetic landscapes of inter-β-strand interactions. Different types of variations show divergence in the influences on the β-sheet conformational ensembles, which is correlated with the divergent aggregation propensity. Our results highlight the plasticity of conformational ensembles upon mutations and PTMs.