Source and function of ubiquitin-like protein
Eukaryotic proteins can be modified by combining with various small molecular substances or proteins. One of the many modifications is to combine with ubiquitin or ubiquitin-like protein (UBL), which can regulate a variety of physiological processes. UBL proteins control the interaction between modified proteins and other biological macromolecules such as proteasomes or chromatin. Various UBL systems use the corresponding enzymes to catalyze the modification reaction, but most of these modification reactions are temporary. There is increasing evidence that this UBL antigen peptide modification pathway is derived from the sulphur transfer system and related enzymes of prokaryotes. Moreover, among the common ancestors of eukaryotes, proteins similar to UBL ligase and UBL deligase are also widely present. These evidences indicate that the UBL antigen peptide modification system does not originate from eukaryotes.
Proteins in eukaryotic cells undergo a variety of post-translational modifications that greatly extend the functional diversity and dynamics of the protein. Proteins can be modified by attachment to a phosphate group, a methylation group, an acetyl group, or certain protein groups, which are typically transient. The ubiquitin protein modification method was the first one found in the above-mentioned modification method linked to proteins. Now, we have studied this modification pathway very thoroughly. Ubiquitin is a small protein that is very conserved in the eukaryotic world but not in the Eubacteria and Archaea. Ubiquitin proteins can also bind to thousands of different proteins.
The ubiquitination process is a complex process (Background Box 1). The UBL modification pathway is also similar to the ubiquitination modification pathway. Although the enzymes involved in the UBL modification pathway are different, they are all evolutionarily related to the enzymes involved in the ubiquitination pathway. Since ubiquitin and UBL proteins have the same three-dimensional core structure, the β-grasp fold structure, this means that various UBL modification systems are derived from a common ancestor.
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