Fig. 7: Model of UFC1 cis and trans oxyanion holes.
From: UFC1 reveals the multifactorial and plastic nature of oxyanion holes in E2 conjugating enzymes
In the cis mechanism, a charged UFC1 undergoes self-ubiquitination, where a Lys residue on the surface of UFC1 attacks the thioester bond. This generates an oxyanion, which is stabilized by a dedicated oxyanion hole composed of hydrogen bonding via the backbone of L117 and T118. In the case of trans-ufmylation, where UFM1 is transferred to a Lys residue on a substrate, a different oxyanion hole takes on this role. This oxyanion hole involves hydrogen bonding with the backbone of K108 and M109. Specifically, K108 contributes C-alpha hydrogen bonding with the oxyanion.
