Peptides and proteins are self-assembled into β-rich self-assemblies such as amyloids in liquid water environments. Despite its importance, detailed structural analysis of this class is hindered by their insoluble and heterogeneous nature. For circumventing this problem, we designed a peptide self-assembly mimic (PSAM) that consists of a central single-layer β-sheet (SLB) capped by terminal domains. In a previous study, we grafted part of an amyloid forming chameleon sequence into a PSAM (termed PSAM-VLGDV1) and found a β-sheet bending at SLB induced by the grafted sequence using x-ray crystallography (Hori et al., 2019 ). Later, we found that another crystal structure of PSAM-VLGDV1 obtained from an isomorphous crystal had a different conformation and we gained an interest in the structural differences of PSAMs within isomorphous crystals. Herein, we report the structural variations trapped within isomorphous crystals by comprehensive structure determinations. Additionally, we demonstrate the structural plasticity of PSAM-VLGDV1 via molecular dynamics simulations. Hydration structure analysis revealed that water molecule locates on the β-sheet surface is important for its plasticity. Our findings suggest that a marginal structural difference can be trapped at the time of crystal core formation, which propagates during crystal growth. Our results suggest that structural plasticity of β-sheet would play an important role in the macroscopic shape formation of peptide self-assemblies.
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