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 Å from native and selenomethionine‐derivative protein crystals, respectively. The crystals belonged to space group C2221, with unit‐cell parameters a = 47.465, b = 97.574, c = 249.215 Å for the native crystals.