title: PEG-protein interaction induced contraction of NalD chains.
abstract: In a recent attempt to crystallize a regulator of MexAB-OprM multi-drug efflux systems in Pseudomonas aeruginosa (NalD), we found that adding polyethylene glycol (PEG3350, Mw = 3,350 g/mol) into the protein solution increases the speed of NalD migration in gel electrophoresis, signaling a smaller hydrodynamic size. At first we conjectured that NalD was degraded unexpectedly by PEG; however, we found that there was no change in its molar mass by MALDI-TOF characterization. Moreover, we found that adding polyacrylic acid (PAA) into the solution mixture returned the NalD migration to its normal speed. Furthermore, our analytic ultracentrifugation and dynamic laser light scattering results directly reveal that NalD interacts with PEG so that individual NalD chains gradually shrink as more PEG chains are added in the range of 10-50 mg/mL. Size exclusion chromatography also confirms that the NalD chain shrinks in the presence of PEG. A combination of these results indicates that PEG3350 chains can complex with NalD to induce an intra-protein chain contraction, presumably via the formation of hydrogen bond between -C-O-C- on PEG and -COOH on NalD, resulting in a smaller hydrodynamic size (faster migration) and a higher apparent molar mass. Note that because the presence of PEG affects osmotic pressure, it is considered to be a precipitator of protein crystallization. Our current finding reveals that the interaction of PEG/protein may play a significant role in protein crystallization. The complexation potentially makes the protein chain segments less flexible, and consequently makes crystallization easier. Hopefully, our current results will stimulate further studies in this direction.
authors.affiliation: Department of Chemical Physics, University of Science and Technology of China, Hefei, China; Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, China.
authors.forename: Jiyan
authors.initials: J
authors.lastname: Yu
authors.affiliation: Department of Chemical Physics, University of Science and Technology of China, Hefei, China; Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, China.
authors.forename: Weizhong
authors.initials: W
authors.lastname: Chen
authors.affiliation: Department of Chemical Physics, University of Science and Technology of China, Hefei, China; Department of Chemistry, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Chi
authors.initials: C
authors.lastname: Wu
authors.affiliation: Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, China.
authors.forename: Hao
authors.initials: H
authors.lastname: Chen
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D057446:Hydrodynamics; D008958:Models, Molecular; D011092:Polyethylene Glycols / Q000378:metabolism* / Q000494:pharmacology*; D011485:Protein Binding; D011487:Protein Conformation / Q000187:drug effects; D011550:Pseudomonas aeruginosa
chemical_list: D001426:Bacterial Proteins; D011092:Polyethylene Glycols