Crystallization and preliminary X‐ray diffraction studies of the WW4 domain of the Nedd4‐2 ubiquitin–protein ligase

Ubiquitin‐mediated protein modification via covalent attachment of ubiquitin has emerged as one of the most common regulatory processes in all eukaryotes. Nedd4‐2, closely related to neuronal precursor cell‐expressed developmentally down‐regulated 4 (Nedd4), is a multimodular ubiquitin–protein ligase comprised of four WW domains and a Hect domain. The WW domains recognize the proline‐rich motifs on the multi‐subunit amiloride‐sensitive epithelial sodium channel (ENaC). To gain insights into the binding of the WW domain to proline‐rich peptides, a protein fragment (78 amino acids) containing the fourth WW domain (WW4) of the Nedd4‐2 protein was purified and crystallized and X‐ray diffraction data were collected. A data set was obtained to 2.5 Å resolution from a cryocooled single crystal at a synchrotron source. The crystals belong to the tetragonal space group P 4 1 2 1 2 (or P 4 3 2 1 2), with unit‐cell parameters a  =  b  = 113.43, c = 103.21 Å. Analysis of the self‐rotation function suggests the presence of four WW4 molecules in the asymmetric unit, with a high unit‐cell solvent content of 74%.