title: The exclusion of glycine betaine from anionic biopolymer surface: why glycine betaine is an effective osmoprotectant but also a compatible solute.
abstract: Paradoxically, glycine betaine (N,N,N-trimethyl glycine; GB) in vivo is both an effective osmoprotectant (efficient at increasing cytoplasmic osmolality and growth rate) and a compatible solute (without deleterious effects on biopolymer function, including stability and activity). For GB to be an effective osmoprotectant but not greatly affect biopolymer stability, we predict that it must interact very differently with folded protein surface than with that exposed in unfolding. To test this hypothesis, we quantify the preferential interaction of GB with the relatively uncharged surface exposed in unfolding the marginally stable lacI helix-turn-helix (HTH) DNA binding domain using circular dichroism and with the more highly charged surfaces of folded hen egg white lysozyme (HEWL) and bovine serum albumin (BSA) using all-gravimetric vapor pressure osmometry (VPO) and compare these results with results of VPO studies (Hong et al. (2004), Biochemistry, 43, 14744-14758) of the interaction of GB with polyanionic duplex DNA. For these four biopolymer surfaces, we observe that the extent of exclusion of GB per unit of biopolymer surface area increases strongly with increasing fraction of anionic oxygen (protein carboxylate or DNA phosphate) surface. In addition, GB is somewhat more excluded from the surface exposed in unfolding the lacI HTH and from the folded surface of HEWL than expected from their small fraction of anionic surface, consistent with moderate exclusion of GB from polar amide surface, as predicted by the osmophobic model of protein stability (Bolen and Baskakov (2001) J. Mol. Biol. 310, 955-963). Strong exclusion of GB from anionic surface explains how it can be both an effective osmoprotectant and a compatible solute; analysis of this exclusion yields a lower bound on the hydration of anionic protein carboxylate surface of two layers of water (>or=0.22 H(2)O A(-)(2)).
authors.affiliation: Department of Biochemistry, Program in Biophysics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Felitsky
authors.forename: Jonathan G
authors.initials: JG
authors.lastname: Cannon
authors.forename: Michael W
authors.initials: MW
authors.lastname: Capp
authors.forename: Jiang
authors.initials: J
authors.lastname: Hong
authors.forename: Adam W
authors.initials: AW
authors.lastname: Van Wynsberghe
authors.forename: Charles F
authors.initials: CF
authors.lastname: Anderson
authors.forename: M Thomas
authors.initials: MT
authors.lastname: Record
mesh_terms: D000838:Anions / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001622:Betaine / Q000737:chemistry* / Q000378:metabolism*; D001704:Biopolymers / Q000737:chemistry / Q000378:metabolism; D002942:Circular Dichroism; D019277:Entropy; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D019077:Helix-Turn-Helix Motifs; D056968:Lac Repressors; D008956:Models, Chemical; D009113:Muramidase / Q000737:chemistry; D009994:Osmolar Concentration; D017510:Protein Folding; D012097:Repressor Proteins / Q000737:chemistry / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000737:chemistry; D012996:Solutions; D013499:Surface Properties; D013696:Temperature
chemical_list: D000838:Anions; D001426:Bacterial Proteins; D001704:Biopolymers; D029968:Escherichia coli Proteins; D056968:Lac Repressors; D012097:Repressor Proteins; D012996:Solutions; D012710:Serum Albumin, Bovine; D001622:Betaine; C421864:hen egg lysozyme; D009113:Muramidase