The article provides a comprehensive overview of the mechanisms and functions of E1 enzymes in the activation and coordination of ubiquitin-like protein (UBL) conjugation pathways. E1 enzymes initiate UBL conjugation by activating UBLs through C-terminal adenylation and thiol transfer, and then charging cognate E2 enzymes to coordinate downstream ubiquitylation pathways. The review highlights the structural and enzymatic mechanisms of E1 enzymes, including the role of the adenylation domain, catalytic Cys domain, and ubiquitin-fold domain (UFD) in UBL activation and transfer to E2 enzymes. It also discusses the diversity and specificity of E1 enzymes, their regulation in vivo, and the development of specific inhibitors for therapeutic applications. The article emphasizes the importance of UBLs in various biological processes and diseases, such as cancer, neurodegenerative disorders, and muscle atrophy, and explores the evolution of E1 enzymes from prokaryotic biosynthetic pathways.The article provides a comprehensive overview of the mechanisms and functions of E1 enzymes in the activation and coordination of ubiquitin-like protein (UBL) conjugation pathways. E1 enzymes initiate UBL conjugation by activating UBLs through C-terminal adenylation and thiol transfer, and then charging cognate E2 enzymes to coordinate downstream ubiquitylation pathways. The review highlights the structural and enzymatic mechanisms of E1 enzymes, including the role of the adenylation domain, catalytic Cys domain, and ubiquitin-fold domain (UFD) in UBL activation and transfer to E2 enzymes. It also discusses the diversity and specificity of E1 enzymes, their regulation in vivo, and the development of specific inhibitors for therapeutic applications. The article emphasizes the importance of UBLs in various biological processes and diseases, such as cancer, neurodegenerative disorders, and muscle atrophy, and explores the evolution of E1 enzymes from prokaryotic biosynthetic pathways.