Letters to Nature

Nature 414, 325-329 (15 November 2001) | doi:10.1038/35104586; Received 19 July 2001; Accepted 11 September 2001

Mechanism of ubiquitin activation revealed by the structure of a bacterial MoeB–MoaD complex

Michael W. Lake1, Margot M. Wuebbens2, K. V. Rajagopalan2 & Hermann Schindelin1

  1. Department of Biochemistry and Center for Structural Biology, State University of New York at Stony Brook, Stony Brook, New York 11794-5115, USA
  2. Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA

Correspondence to: Hermann Schindelin1 Correspondence and requests for materials should be addressed to H.S. (e-mail: hermann.schindelin@sunysb.edu). The atomic coordinates have been deposited in the Protein Data Bank under accessions numbers 1JW9, 1JWA and 1JWB.

The activation of ubiquitin and related protein modifiers1, 2 is catalysed by members of the E1 enzyme family that use ATP for the covalent self-attachment of the modifiers to a conserved cysteine. The Escherichia coli proteins MoeB and MoaD are involved in molybdenum cofactor (Moco) biosynthesis, an evolutionarily conserved pathway3, 4. The MoeB- and E1-catalysed reactions are mechanistically similar, and despite a lack of sequence similarity, MoaD and ubiquitin display the same fold including a conserved carboxy-terminal Gly-Gly motif5. Similar to the E1 enzymes, MoeB activates the C terminus of MoaD to form an acyl-adenylate. Subsequently, a sulphurtransferase converts the MoaD acyl-adenylate to a thiocarboxylate that acts as the sulphur donor during Moco biosynthesis6, 7. These findings suggest that ubiquitin and E1 are derived from two ancestral genes closely related to moaD and moeB 3, 5. Here we present the crystal structures of the MoeB–MoaD complex in its apo, ATP-bound, and MoaD-adenylate forms, and highlight the functional similarities between the MoeB– and E1–substrate complexes. These structures provide a molecular framework for understanding the activation of ubiquitin, Rub, SUMO and the sulphur incorporation step during Moco and thiamine biosynthesis.