Crystallization and preliminary X-ray analysis of the bacterial ATP-binding-cassette (ABC) protein MalK

The ATP-binding protein, MalK, of the bacterial ABC (ATP-binding-cassette) transport complex MalFGK₂ provides the energy for the translocation of maltose and maltodextrins across the cytoplasmic membrane. The MalK protein from Salmonella typhimurium was overexpressed in Escherichia coli and crystallized by the hanging-drop method using (NH₄)₂SO₄ as a precipitant. The crystals belong to space group P6_x22 (most probably x = 1 or 5) with cell dimensions a = 181.8 and c = 182.5 Å, corresponding to three or four molecules per asymmetric unit. They diffract to a resolution of about 3 Å on a synchrotron X-­ray source and are suitable for structure determination.