Structural Insights into the Trimeric Assembly of the HERC5 HECT Domain through SAXS Analysis

HERC5 is an interferon-induced E3 ubiquitin ligase involved in ISGylation, a crucial post-translational modification regulating antiviral responses. The HECT domain of HERC5 plays a key role in substrate recognition and ubiquitin transfer. The HERC protein family is structurally characterized by containing the C-terminal HECT (Homologous to the E6-AP Carboxyl Terminus) domain and N-terminal RCC1-like ( The Regulator of Chromosome Condensation 1) domains. In spite of this, the HECT domain-specific oligomerization capacity of HERC5 is not fully clarified. Here, we investigate the oligomeric state of the HERC5 HECT domain in solution, using affinity and size-exclusion chromatography, followed by SAXS measurements at 2.0 mg/ml and 10°C. SAXS data analysis revealed a trimeric assembly, supported by Guinier and Kratky analyses, distance distribution functions, and ab initio modeling. These findings suggest that trimerization may play a regulatory role in HERC5 function, contributing to a broader understanding of HECT-type E3 ligase mechanisms.