Recent experimental studies have shown that amyloid fi bril formed by aggregation of β peptide exhibits excellent mechanical properties comparable to other protein materials such as actin fi laments and microtubules. These excellent mechanical properties of amyloid fi brils are related to their functional role in disease expression. This indicates the necessity of understanding how an amyloid fi bril achieves the remarkable mechanical properties through self-aggregation with structural hierarchy. However, the structure-property-function relationship still remains elusive. In this work, the mechanical properties of human islet amyloid polypeptide (hIAPP) are studied with respect to its structural hierarchies and structural shapes by coarse-grained normal mode analysis. The simulation shows that hIAPP fi bril can achieve the excellent bending rigidity via specifi c aggregation patterns such as antiparallel stacking of β peptides. Moreover, the length-dependent mechanical properties of amyloids are found. This length-dependent property has been elucidated from a Timoshenko beam model that takes into account the shear effect on the bending of amyloids. In summary, the study sheds light on the importance of not only the molecular architecture, which encodes the mechanical properties of the fi bril, but also the shear effect on the mechanical (bending) behavior of the fi bril.

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