The increase in salt concentration decreased ThT fluorescence, suggesting the significance of electrostatic interactions (Supplementary Fig. ). Adenosine diphosphate (ADP) significantly increased ThT fluorescence, while neither adenosine monophosphate (AMP) nor phosphate showed enhancement (Fig. ). This trend indicates that multivalent anions may have prompted the fibril formation of YK13. Unexpectedly, the addition of pyrophosphate did not increase ThT fluorescence. Furthermore, uridine triphosphate (UTP) and cytidine triphosphate (CTP) showed no significant impact (Supplementary Fig. ). In contrast, guanosine triphosphate (GTP), containing a purine base, exhibited strong intensity comparable to that upon ATP addition. These results underscore the contribution of purine bases to peptide self-assembly. On the basis of these considerations, MD simulations were performed to explore the impact of ATP on YK13 assembly. The simulations revealed that, in the presence of ATP, the YK13 fibril structure was well maintained (RMSD = 2.2 Å) (Fig. and Supplementary Fig. ). Notably, the 100 ns structure illustrated the base stacking of ATP on the peptides. In contrast, in the absence of ATP, the YK13 fibers rapidly collapsed. These findings strongly suggest that ATP-mediated YK peptide fiber formation relies on multivalent electrostatic interactions involving triphosphate and lysine, as well as base-stacking interactions among ATPs.