Purification, crystallization and preliminary X-ray diffraction analysis of a variant of the ColE1 Rop protein

Rop is the paradigm of a canonical four-α-helical bundle. Its loop region has attracted considerable interest because a single alanine-to-proline substitution (A31P) in the loop is sufficient to change the topology of this small protein. In order to further analyse the loop region as a possible folding-control element, the double mutant D30P/A31G (RopPG) was produced, purified and crystallized. The crystals belonged to space group P2₁, with unit-cell parameters a = 26.7, b = 38.8, c = 56.6 Å, β = 100.9° and two molecules in the asymmetric unit. A complete data set was collected at 100 K to a resolution of 1.4 Å using synchrotron radiation.