NEDD8-UBA3:NAE1 binds a second NEDD8

After covalent attachment of the first NEDD8 molecule to the catalytic cysteine, a second NEDD8 binds to the now-free adenylation site on the UBA3 subunit of UBA3:NAE1. This 'doubly-loaded' E1 enzyme is primed to transfer the covalently-bound NEDD8 to the downstream E2 enzyme (Huang et al, 2005; Huang et al, 2007; reviewed in Enchev et al, 2015). Note that although not depicted here, the second NEDD8 moiety is covalently adenylated at its C-terminal glycine residue at the end of this reaction.

在首个NEDD8分子通过共价键与催化位点上的半胱氨酸结合之后，第二个NEDD8分子随即与如今释放的腺苷酸化位点结合于UBA3:NAE1亚单位的UBA3部分。此‘双重装载’的E1酶处于准备状态，以将共价结合的NEDD8转移至下游的E2酶（参见Huang等人，2005；Huang等人，2007；Enchev等人，2015年综述）。请注意，尽管此处未展示，第二个NEDD8分子在其反应结束时的C端甘氨酸残基处也通过共价键完成腺苷酸化。