@phdthesis{LiessneeEller2021,
  author    = {Liess [n{\´e}e Eller], Anna Katharina Luise},
  title     = {Understanding the regulation of the ubiquitin-conjugating enzyme UBE2S},
  doi       = {10.25972/OPUS-20419},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204190},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {The ubiquitination of proteins serves as molecular signal to control an enormous number of physiological processes and its dysregulation is connected to human diseases like cancer. The versatility of this signal stems from the diverse ways by which ubiquitin can be attached to its targets. Thus, specificity and tight regulation of the ubiquitination are pivotal requirements of ubiquitin signaling. Ubiquitin-conjugating enzymes (E2s) act at the heart of the ubiquitination cascade, transferring ubiquitin from a ubiquitin-activating enzyme (E1) to a ubiquitin ligase (E3) or substrate. When cooperating with a RING-type E3, ubiquitin-conjugating enzymes can determine linkage specificity in ubiquitin chain formation. Our understanding of the regulation of E2 activities is still limited at a structural level. The work described here identifies two regulation mechanisms in UBE2S, a cognate E2 of the human RING-type E3 anaphase-promoting complex/cyclosome (APC/C). UBE2S elongates ubiquitin chains on APC/C substrates in a Lys11 linkage-specific manner, thereby targeting these substrates for degradation and driving mitotic progression. In addition, UBE2S was found to have a role in DNA repair by enhancing non-homologous end-joining (NHEJ) and causing transcriptional arrest at DNA damage sites in homologous recombination (HR). Furthermore, UBE2S overexpression is a characteristic feature of many cancer types and is connected to poor prognosis and diminished response to therapy. The first regulatory mechanism uncovered in this thesis involves the intramolecular auto-ubiquitination of a particular lysine residue (Lys+5) close to the active site cysteine, presumably through conformational flexibility of the active site region. The Lys+5-linked ubiquitin molecule adopts a donor-like, 'closed' orientation towards UBE2S, thereby conferring auto-inhibition. Notably, Lys+5 is a major physiological ubiquitination site in ~25\% of the human E2 enzymes, thus providing regulatory opportunities beyond UBE2S. Besides the active, monomeric state and the auto-inhibited state caused by auto-ubiquitination, I discovered that UBE2S can adopt a dimeric state. The latter also provides an auto-inhibited state, in which ubiquitin transfer is blocked via the obstruction of donor binding. UBE2S dimerization is promoted by its unique C-terminal extension, suppresses auto-ubiquitination and thereby the proteasomal degradation of UBE2S. Taken together, the data provided in this thesis illustrate the intricate ways by which UBE2S activity is fine-tuned and the notion that structurally diverse mechanisms have evolved to restrict the first step in the catalytic cycle of E2 enzymes.},
  subject      = {E2},
  language  = {en}
}