Purification, crystallization and preliminary X-ray crystallographic studies of the complex between Smc5 and the SUMO E3 ligase Mms21.

Smc5/6, a protein complex that belongs to the structural maintenance of chromosome (SMC) family, plays a key role in DNA replication, sister chromatid recombination and DNA damage repair. The complex contains eight subunits, including a SUMO E3 ligase Mms21 (Nse2). The activity of Mms21 is important for regulation of Smc5/6 in the response to DNA damage. Mms21 and the Mms21-binding region of Smc5 were overexpressed and purified individually in Escherichia coli with a C-terminal LEHHHHHH tag. The Mms21-Smc5 protein complex was crystallized. The diffraction of the crystals was improved greatly by glutaraldehyde treatment. X-ray diffraction data sets were collected to resolutions of 2.3 and 3.9 A from native and selenomethionine-derivative protein crystals, respectively. The crystals belonged to space group C222(1), with unit-cell parameters a = 47.465, b = 97.574, c = 249.215 A for the native crystals.