The combination of an E2 ubiquitin-conjugating enzyme with an E3 ubiquitin-ligase is essential for ubiquitin modification of a substrate. Moreover, the pairing dictates both the substrate choice and the modification type. The molecular details of generic E3-E2 interactions are well established. Nevertheless, the determinants of selective, specific E3-E2 recognition are not understood. There are ~40 E2s and ~600 E3s giving rise to a possible ~24,000 E3-E2 pairs. Using the Fanconi Anemia pathway exclusive E3-E2 pair, FANCL-Ube2T, we report the atomic structure of the FANCL RING-Ube2T complex, revealing a specific and extensive network of additional electrostatic and hydrophobic interactions. Furthermore, we show that these specific interactions are required for selection of Ube2T over other E2s by FANCL.
Hodson, C., Purkiss, A., Miles, J. A., & Walden, H. (2014). Structure of the Human FANCL RING-Ube2T Complex Reveals Determinants of Cognate E3-E2 Selection. Structure, 22(2), 337-344. https://doi.org/10.1016/j.str.2013.12.004