title: D-alanine-D-alanine ligase (ADP) from Salmonella typhimurium. Overproduction, purification, crystallization and preliminary X-ray analysis.
abstract: The ddlA gene from Salmonella typhimurium coding for D-alanine-D-alanine ligase (ADP-forming) has been subcloned behind the tac promotor in the plasmid pKK223-3, with expression in Escherichia coli JM105. The overexpression system yields 58 mg of active enzyme from 12 g of wet cell paste after 40-fold purification to homogeneity. 5,5'-Dithiobis-(2-nitrobenzoic acid) titrations indicate that all four cysteine residues exist as free thiols. Two crystal forms of the 39,300 Mr enzyme have been produced. A tetragonal form grows at 21 degrees C from 10 to 15% (w/v) polyethylene glycol 8000 in space group P4(1)2(1)2, with two molecules in the asymmetric unit; it has cell constants a = b = 83.8 A, c = 220.0 A, and diffracts to 2.9 A. A monoclinic form grows from 30% (w/v) ammonium sulfate in space group P2(1), with two molecules in the asymmetric unit; it has cell constants a = 60.4 A, b = 102.1 A, c = 64.3 A, beta = 115.7 degrees, and diffracts to 2.2 A resolution.
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs 06268.
authors.forename: J R
authors.initials: JR
authors.lastname: Knox
authors.forename: H S
authors.initials: HS
authors.lastname: Liu
authors.forename: C T
authors.initials: CT
authors.lastname: Walsh
authors.forename: L E
authors.initials: LE
authors.lastname: Zawadzke
mesh_terms: D003001:Cloning, Molecular; D003460:Crystallization; D010453:Peptide Synthases / Q000096:biosynthesis* / Q000302:isolation & purification; D012486:Salmonella typhimurium; D014961:X-Ray Diffraction
chemical_list: D010453:Peptide Synthases; C019638:D-alanylalanine synthetase