Peptides are small proteins that act as messengers, sending signals by binding...

https://yourhealthmagazine.net/article/health-news-research/how-peptides-help-scientists-understand-cell-communication/

Peptides are small proteins that act as messengers, sending signals by binding to specific receptors on cells. Researchers use peptides to study how receptors work, which ones they prefer (selectivity), and the signaling pathways they trigger