page_title: Ubiquitin-like protein
section_title: Evolution
hierarchical_section_title: Ubiquitin-like protein / Evolution
caption_attribution_description: English: Superposition of ubiquitin (PDB: 1UBQ&#8203;, green​) and bacterial sulfur transfer protein MoaD (PDB: 1FM0&#8203; chain D, light gray​) illustrating their structural similarity. Rendered using PyMOL.
context_page_description: Ubiquitin-like proteins are a family of small proteins involved in post-translational modification of other proteins in a cell, usually with a regulatory function. The UBL protein family derives its name from the first member of the class to be discovered, ubiquitin, best known for its role in regulating protein degradation through covalent modification of other proteins. Following the discovery of ubiquitin, many additional evolutionarily related members of the group were described, involving parallel regulatory processes and similar chemistry. UBLs are involved in a widely varying array of cellular functions including autophagy, protein trafficking, inflammation and immune responses, transcription, DNA repair, RNA splicing, and cellular differentiation.
context_section_description: The evolution of UBLs and their associated suites of regulatory proteins has been of interest since shortly after they were recognized as a family. Phylogenetic studies of the beta-grasp protein fold superfamily suggest that eukaryotic UBLs are monophyletic, indicating a shared evolutionary origin. UBL regulatory systems - including UBLs themselves and the cascade of enzymes that interact with them - are believed to share a common evolutionary origin with prokaryotic biosynthesis pathways for the cofactors thiamine and molybdopterin; the bacterial sulfur transfer proteins ThiS and MoaD from these pathways share the beta-grasp fold with UBLs, while sequence similarity and a common catalytic mechanism link pathway members ThiF and MoeB to ubiquitin-activating enzymes. Interestingly, the eukaryotic protein URM1 functions as both a UBL and a sulfur-carrier protein, and has been described as a molecular fossil establishing this evolutionary link.
  Comparative genomics surveys of UBL families and related proteins suggest that UBL signaling was already well-developed in the last eukaryotic common ancestor and ultimately originates from ancestral archaea, a theory supported by the observation that some archaeal genomes possess the necessary genes for a fully functioning ubiquitination pathway. Two different diversification events within the UBL family have been identified in eukaryotic lineages, corresponding to the origin of multicellularity in both animal and plant lineages.
caption: Superposition of the structures of ubiquitin (PDB: 1UBQ​, green) and MoaD (PDB: 1FM0​, light gray)
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