title: Crystallographic structure of ubiquitin in complex with cadmium ions.
abstract: BACKGROUND
  Ubiquitination plays a critical role in regulating many cellular processes, from DNA repair and gene transcription to cell cycle and apoptosis. It is catalyzed by a specific enzymatic cascade ultimately leading to the conjugation of ubiquitin to lysine residues of the target protein that can be the ubiquitin molecule itself and to the formation of poly-ubiquitin chains.
  
  
  RESULTS
  We present the crystal structure at 3.0 A resolution of bovine ubiquitin crystallized in presence of cadmium ions. Two molecules of ubiquitin are present in the asymmetric unit. Interestingly this non-covalent dimeric arrangement brings Lys-6 and Lys-63 of each crystallographically-independent monomer in close contact with the C-terminal ends of the other monomer. Residues Leu-8, Ile-44 and Val-70 that form a hydrophobic patch at the surface of the Ub monomer are trapped at the dimer interface.
  
  
  CONCLUSIONS
  The structural basis for signalling by poly-Ub chains relies on a visualization of conformations of alternatively linked poly-Ub chains. This arrangement of ubiquitin could illustrate how linkages involving Lys-6 or Lys-63 of ubiquitin are produced in the cell. It also details how ubiquitin molecules can specifically chelate cadmium ions.
authors.affiliation: School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, 637551, Singapore.
authors.forename: Insaf A
authors.initials: IA
authors.lastname: Qureshi
authors.forename: Francois
authors.initials: F
authors.lastname: Ferron
authors.forename: Cheah Chen
authors.initials: CC
authors.lastname: Seh
authors.forename: Peter
authors.initials: P
authors.lastname: Cheung
authors.forename: Julien
authors.initials: J
authors.lastname: Lescar