Post-translational modifications of ubiquitin to target proteins alter their structure, function, and/or localization
Ubiquitination modifications are one of the most important post-translational modifications and play an important role in many cellular processes and are performed through a sequential enzyme cascade of E1-activating
enzymes, E2-binding enzymes, and E3 ligases.
In the past, UBA1 was considered to be the only E1 that activates ubiquitin until 2007, when a second ubiquitin-activating enzyme was discovered—a protein called UBA6 that is found only in vertebrates and sea urchins and has 40% sequence homology
UBA6 is an unusual E1 enzyme because of its dual specificity, activating both ubiquitin and ubiquitin-like protein (Ubl) FAT10 (also known as ubiquitin D
UBA6 is the only E1 that catalyzes FAT10
Since UBA6-mediated ubiquitination and FAT10 are involved in various cellular processes in physiological and pathophysiological environments, it is not surprising that the failure of one or more components of the system can lead to various diseases
UBA6 was found to be overexpressed
in the brains of Alzheimer's patients.
The tumor suppressor protein p53 is the substrate of FAT10, and the study found that the double negative regulation of FAT10 and p53 plays a key role in controlling tumorigenesis, which is consistent
with the phenomenon of FAT10 being overexpressed in multiple cancer cell types.
This makes UBA6 an attractive potential drug target, however, the dual specificity of UBA6 complicates
To further explore targeted inhibition of UAB6, it is necessary to understand its dual specificity and identify which variants of UAB6 cause its ubiquitin deficiency or FAT10 deficiency
Professor Hermann Schindelin's research team at the Rudolf Virchow Center at the University of Würzburg has reported for the first time the crystal structure
of UBA6 composite with ATP or FAT10.
Interestingly, their structural and modeling studies also revealed the dual recognition mechanism
of UBA6 for ubiquitin and FAT10.
Another key finding was to identify which mutations cause selective deficiencies
in UBA6 to ubiquitin or FAT10.
"These results provide a basis
for studying the individual role of UBA6 in ubiquitin or FAT10 activation in downstream cell pathways," Schindelin said.
A key to the study is to identify UBA6 mutations
that can cause UBA6 selective FAT10 deficiency or ubiquitin deficiency.
Specifically, by modeling the UBA6-ubiquitin complex and comparing it with the UBA1-ubiquitin structure, it was determined that the E601 site of UBA6, when replaced with Gln, would seriously impair the ubiquitination function of UBA6 without interfering with FAT10 activation
Mutations at the D616A site also lead to UBA6-mediated ubiquitination defects
These two UBA6 variants can be used to study the effects
of UBA6-mediated ubiquitination.
By combining these two variants, more effective inhibition can be obtained
Instead, the structure of the UBA6-FAT10 complex reveals the interaction between the N-terminal of FAT10 and the 3HB of UBA6, which is primarily driven
by electrostatic interactions.
The group charge reversal mutation in UBA6 disrupts this interacting interface and prevents UBA6 from activating FAT10
Therefore, UBA6 charge inversion is an important tool
for studying the effects of UBA6-mediated FAT10.
These mutants will be an important tool
for describing the physiological consequences of UBA6-catalyzed ubiquitination or FAT10ization.
UBA6 gene knockout interferes with both processes at the same time, and now it is now possible to selectively turn off either and study the physiological consequences of the resulting.
Future studies of UBA6 selectively impaired mutants are needed to investigate the possible link
between UBA6-catalyzed ubiquitination and FAT10 in cancer.