title: Effect of NaCl on the conformational stability of the thermophilic γ-glutamyltranspeptidase from Geobacillus thermodenitrificans: Implication for globular protein halotolerance.
abstract: The transpeptidation activity of γ-glutamyltranspeptidase from Geobacillus thermodenitrificans (GthGT) is negligible and the enzyme is highly thermostable. Here we have examined the effect of concentrated NaCl solutions on structure, stability, dynamics and enzymatic activity of GthGT. The protein exhibited hydrolytic activity over a broad range of NaCl concentrations. Even at 4.0M NaCl, GthGT retained more than 90% of the initial activity and showed unaltered fluorescence emission, secondary structure and acrylamide quenching on tryptophan fluorescence. Furthermore, at 2.8M and 4.0M NaCl the temperature-induced unfolding profiles are dramatically changed with large (>20°C) positive shifts in the denaturation temperature. These features make GthGT an ideal system to be used in industrial processes that require high temperatures and high-salt environments. A general explanation of the NaCl effect by means of a statistical thermodynamic model is also provided, together with an analysis of residue distribution between protein surface and interior in 15 non-redundant families of halophilic and non-halophilic proteins. The results are in line with a comparative sequence and structural analysis between halophilic and non-halophilic γ-glutamyltranspeptidases which revealed that a major role in halotolerance should be played by solvent exposed negatively charged residues.
authors.affiliation: Department of Chemical Sciences, University of Naples Federico II, Naples, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Pica
authors.forename: Irene
authors.initials: I
authors.lastname: Russo Krauss
authors.forename: Immacolata
authors.initials: I
authors.lastname: Castellano
authors.forename: Francesco
authors.initials: F
authors.lastname: La Cara
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Graziano
authors.forename: Filomena
authors.initials: F
authors.lastname: Sica
authors.forename: Antonello
authors.initials: A
authors.lastname: Merlino
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D004795:Enzyme Stability / Q000502:physiology; D056506:Geobacillus / Q000201:enzymology*; D017433:Protein Structure, Secondary; D012965:Sodium Chloride / Q000737:chemistry*; D005723:gamma-Glutamyltransferase / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D012965:Sodium Chloride; D005723:gamma-Glutamyltransferase