Structural and Mechanistic Characterization of HERC2 E3 Ubiquitin Ligase C‐lobe with Implications in Cancer, Prader‐Willi Syndrome, and Eye Color

HERC2 (HECT domain containing and RCC1‐like domain containing E3 ubiquitin ligase 2) is a HECT E3 ubiquitin protein ligase that is implicated in breast cancer, Prader‐Willi syndrome, and eye color. HECT E3 ubiquitin ligases covalently attach ubiquitin onto substrates to target proteins for proteasomal degradation, initiate DNA damage repair, control cell cycle and intracellular trafficking, and regulate transcription. HERC2 has proposed implications with DNA damage repair and proteasomal degradation. The HERC2 gene has been linked to the neurodevelopmental disorder Prader‐Willi syndrome and is part of the cis‐regulatory module for OCA2 (oculocutaneous albinism 2). To date, only a few substrates of HERC2 have been identified including BRCA1 (breast cancer 1). Using biochemical and biophysical techniques, such as circular dichroism and multidimensional heteronuclear NMR spectroscopy, the HERC2 C‐lobe structure was characterized. Our studies show that HERC2 is mainly α‐helical with a flexible acidic C‐terminal tail extension. We demonstrate that the C‐terminal tail extension is important for polyubiquitin chain formation through intramolecular interactions with ubiquitin. The truncation of the HERC2 C‐terminal tail decreases protein stability and function. These structural and mechanistic studies on the HERC2 C‐lobe are important for elucidating the cellular role of HERC2 along with its implications with disease. Support or Funding Information NIH‐NIGMS FundingAbbVie summer research grantClark University