60th residues of ubiquitin and Nedd8 are located out of E2-binding surfaces, but are important for K48 ubiquitin-linkage.
Choi, Y.S., Jeon, Y.H., Ryu, K.S., Cheong, C.(2009) FEBS Lett 583: 3323-3328
- PubMed: 19782077 
- DOI: https://doi.org/10.1016/j.febslet.2009.09.034
- Primary Citation of Related Structures:  
2KO3 - PubMed Abstract: 
Nedd8, a ubiquitin-like modifier, is covalently attached to various proteins. Although Nedd8 has higher sequence identity (57%) with ubiquitin, its conserved K48 residue cannot form covalent linkage with ubiquitin. To decipher the reason why Nedd8 cannot be an effective ubiquitin-acceptor, we compared the non-covalent interaction between Nedd8 and ubiquitin for various E2s using cross-saturation NMR technique. However, both Nedd8 and ubiquitin displayed almost identical non-covalent E2-binding properties. The K60 of Nedd8 was not present at the E2-binding surface, but its mutation to Asn converted Nedd8 into a ubiquitin-acceptor. The N60 ubiquitin mutants also displayed a decreased ubiquitin-accepting activity. These results suggest the presence of an uncharacterized determinant for the K48 ubiquitin-linkage that is not related to non-covalent E2-bindings.
Organizational Affiliation: 
Division of Magnetic Resonance, Korea Basic Science Institute Ochang Campus, Cheongwon-Gun, Ochang-Eup, Yangcheong-Ri 804-1, Chungcheongbuk-Do 363-883, South Korea.