Cloning expression purification crystallization and preliminary X-ray diffraction analysis of propionate kinase (TdcD) from Salmonella typhimurium

摘要

In the cell, propionate is mainly formed during β-oxidation of odd-numbered carbon-chain fatty acids, fermentation of carbohydrates and degradation of the amino acids threonine, valine, isoleucine and methionine. Recently, it has been shown that l-threonine is non-oxidatively cleaved to propionate via 2-­ketobutyrate. The last step in this process, conversion of propionyl phosphate and ADP to propionate and ATP, is catalysed by propionate kinase (EC 2.7.1.–). Here, the cloning of propionate kinase (molecular weight 44 kDa) from Salmonella typhimurium with an N-terminal hexahistidine affinity tag and its overexpression in Escherichia coli are reported. Purified propionate kinase was found to cocrystallize with ADP in the hanging-drop vapour-diffusion and microbatch methods. Crystals belong to space group P3121 or P3221, with unit-cell parameters a = b = 111.47, c = 66.52 Å. A complete data set to 2.2 Å resolution has been collected using an image-plate detector system mounted on a rotating-anode X-ray generator.