Interfacial interaction and lateral association of cross-seeding assemblies between hIAPP and rIAPP oligomers

Cross-sequence interactions between different amyloid peptides are important not only for the fundamental understanding of amyloid aggregation and polymorphism mechanisms, but also for probing a potential molecular link between different amyloid diseases. Here, we computationally modeled and simulated a series of hybrid hIAPP (human islet amyloid polypeptide)-rIAPP (rat islet amyloid polypeptide) assemblies and probed their structural stability, lateral association, and interfacial interactions using combined peptide-packing search, molecular dynamics (MD) simulations, and the Monte Carlo sampling method. We then identified a number of stable and highly populated hIAPP-rIAPP assemblies at the lowest energy states, in which hIAPP and rIAPP oligomers were stacked laterally on top of each other to form supramolecular beta-sheet double layers in an antiparallel fashion. These hIAPP-rIAPP assemblies adopted different interfaces formed by C-terminal beta-sheets of hIAPP and rIAPP oligomers (hCCr), N-terminal beta-sheets of hIAPP and rIAPP oligomers (hNNr), and alternative N-terminal/C-terminal beta-sheets of hIAPP and rIAPP oligomers (hNCr and hCNr). Different interfaces along with distinct interfacial residue packings provided different driving interfacial forces to laterally associate two beta-sheet layers of hIAPP and rIAPP together for forming polymorphic hIAPP-rIAPP assemblies. Such lateral association between hIAPP and rIAPP not only explained the experimentally observed cross-seeding behavior of hIAPP and rIAPP, but also demonstrated the co-existence of polymorphic amyloid cross-seeding species. A cross-seeding mechanism for hIAPP and rIAPP aggregation was proposed on the basis of our simulated models and experimental data. This work provides a better understanding of cross-seeding aggregation and polymorphism mechanisms of amyloidogenesis.