title: Detection of L-lactate in polyethylene glycol solutions confirms the identity of the active-site ligand in a proline dehydrogenase structure.
abstract: Polyethylene glycol (PEG) is often used in protein crystallography as a low-ionic-strength precipitant for crystallization and as a cryoprotectant for low-temperature data collection. Prompted by the discovery of an apparent L-lactate molecule bound in the active site of the Escherichia coli PutA proline dehydrogenase domain crystal structure, the L-lactate concentration of several PEG solutions was measured. 50%(w/v) solutions of PEGs with molecular weight 3000, 4000 and 8000 contain millimolar levels of L-lactate. In contrast, L-lactate was not detected in solutions of PEG monomethyl ethers or PEG 3350. These results help to explain why L-lactate was present in the proline dehydrogenase domain crystal structure. This work also has implications for the crystallization of enzymes that bind L-lactate.
authors.affiliation: Departments of Chemistry and Biochemistry, University of Missouri-Columbia, Columbia, MO 65211, USA.
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.forename: John J
authors.initials: JJ
authors.lastname: Tanner
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002138:Calibration; D007773:Lactates / Q000032:analysis*; D008024:Ligands; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D011092:Polyethylene Glycols / Q000737:chemistry*; D011394:Proline Oxidase / Q000737:chemistry* / Q000378:metabolism*; D012996:Solutions
chemical_list: D001426:Bacterial Proteins; D007773:Lactates; D008024:Ligands; D008565:Membrane Proteins; C080683:PutA protein, Bacteria; D012996:Solutions; D011092:Polyethylene Glycols; D011394:Proline Oxidase