Multiscale Molecular Simulations Reveal the Structural Pathway of Histatin 1 Self-Association

Histatins are a family of human saliva peptides; the three main members consist of Histatin 1 (Hst1), Histatin 3 (Hst3), and Histatin 5 (Hst5). Despite their high primary-structure similarity, the peptides display varied functions and behaviors. Experimental evidence supports concentration-dependent self-association of Hst1, but the molecular mechanisms remain poorly understood. This property is of interest because it is not observed in Hst5. Here, we combine atomistic and coarse-grained molecular dynamics simulations with a decomposition-based trajectory analysis to investigate the structural origins of Hst1 self-association across multiple length and time scales. Atomistic simulations reveal dimers that remain associated over the simulated time scales, together with transient higher-order oligomers. Analysis of intermolecular residue contacts highlights aromatic residues as prominent contributors to peptide association, consistent with a multivalent interaction network. Coarse-grained simulations extend these observations to larger systems and longer time scales, demonstrating a progressive assembly into dynamic peptide clusters. By discretizing the resulting conformational landscape, we extracted representative structures to reconstruct the self-association pathway from dispersed monomers to higher-order assemblies. The simulations provide a multiscale description of Hst1 self-association and support a model in which weak, multivalent peptide–peptide contacts contribute to the formation of dynamic peptide-rich assemblies. Although the present work does not directly demonstrate liquid–liquid phase separation, it identifies molecular features associated with biomolecular assembly.