Structural Insights into E1-Catalyzed Ubiquitin Activation and Transfer to Conjugating Enzymes

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2008.05.046 Byline: Imsang Lee (1), Hermann Schindelin (1)(2) Keywords: PROTEINS Abstract: Ubiquitin (Ub) and ubiquitin-like proteins (Ubls) are conjugated to their targets by specific cascades involving three classes of enzymes, E1, E2, and E3. Each E1 adenylates the C terminus of its cognate Ubl, forms a E1[approximately equal to]Ubl thioester intermediate, and ultimately generates a thioester-linked E2[approximately equal to]Ubl product. We have determined the crystal structure of yeast Uba1, revealing a modular architecture with individual domains primarily mediating these specific activities. The negatively charged C-terminal ubiquitin-fold domain (UFD) is primed for binding of E2s and recognizes their positively charged first [alpha] helix via electrostatic interactions. In addition, a mobile loop from the domain harboring the E1 catalytic cysteine contributes to E2 binding. Significant, experimentally observed motions in the UFD around a hinge in the linker connecting this domain to the rest of the enzyme suggest a conformation-dependent mechanism for the transthioesterification function of Uba1; however, this mechanism clearly differs from that of other E1 enzymes. Author Affiliation: (1) Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215, USA (2) Rudolf Virchow Center for Experimental Biomedicine and Institute for Structural Biology, University of Wurzburg, Versbacher Str. 9, 97078 Wurzburg, Germany Article History: Received 9 October 2007; Revised 20 March 2008; Accepted 12 May 2008 Article Note: (miscellaneous) Published: July 24, 2008