The activation of the MAPK pathway begins with the binding of a ligand to a cell surface receptor, such as a receptor tyrosine kinase (RTK). This event leads to the dimerization and autophosphorylation of the receptor, creating binding sites for adapter proteins. These adapter proteins, in turn, recruit and activate Ras, a small GTPase. Activated Ras then triggers the activation of MAP3K, which phosphorylates and activates MAP2K. Finally, MAP2K phosphorylates MAPK, leading to the activation of various downstream targets, including transcription factors.
