title: Flexibility and enzyme activity of NADH oxidase from Thermus thermophilus in the presence of monovalent cations of Hofmeister series.
abstract: Recently, we have shown that anions of Hofmeister series affect the enzyme activity through modulation of flexibility of its active site. The enzyme activity vs. anion position in Hofmeister series showed an unusual bell-shaped dependence. In the present work, six monovalent cations (Na(+), Gdm(+), NH(4)(+), Li(+), K(+) and Cs(+)) of Hofmeister series with chloride as a counterion have been studied in relation to activity and stability of flavoprotein NADH oxidase from Thermus thermophilus (NOX). With the exception of strongly chaotropic guanidinium cation, cations are significantly less effective in promoting the Hofmeister effect than anions mainly due to repulsive interactions of positive charges around the active site. Thermal denaturations of NOX reveal unfavorable electrostatic interaction at the protein surface that may be shielded to different extent by salts. Michaelis-Menten constants for NADH, accessibility of the active site as reflected by Stern-Volmer constants and activity of NOX at high cation concentrations (1-2 M) show bell-shaped dependences on cation position in Hofmeister series. Our analysis indicates that in the presence of kosmotropic cations the enzyme is more stable and possibly more rigid than in the presence of chaotropic cations. Molecular dynamic (MD) simulations of NOX showed that active site switches between open and closed conformations [J. Hritz, G. Zoldak, E. Sedlak, Cofactor assisted gating mechanism in the active site of NADH oxidase from Thermus thermophilus, Proteins 64 (2006) 465-476]. Enzyme activity, as well as substrate binding, can be regulated by the salt mediated perturbation of the balance between open and closed forms. We propose that compensating effect of accessibility and flexibility of the enzyme active site leads to bell-shaped dependence of the investigated parameters.
authors.affiliation: Department of Biochemistry, Faculty of Sciences P. J. Safárik University, Kosice, Slovakia.
authors.forename: Kamil
authors.initials: K
authors.lastname: Tóth
authors.forename: Erik
authors.initials: E
authors.lastname: Sedlák
authors.forename: Mathias
authors.initials: M
authors.lastname: Sprinzl
authors.forename: Gabriel
authors.initials: G
authors.lastname: Zoldák
mesh_terms: D002414:Cations, Monovalent / Q000494:pharmacology*; D004795:Enzyme Stability / Q000187:drug effects; D005486:Flavin Mononucleotide / Q000378:metabolism; D005453:Fluorescence; D007700:Kinetics; D008958:Models, Molecular; D009097:Multienzyme Complexes / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D018583:Pliability / Q000187:drug effects; D011489:Protein Denaturation / Q000187:drug effects; D012492:Salts / Q000494:pharmacology; D013379:Substrate Specificity / Q000187:drug effects; D013696:Temperature; D016963:Thermus thermophilus / Q000187:drug effects / Q000201:enzymology*
chemical_list: D002414:Cations, Monovalent; D009097:Multienzyme Complexes; D012492:Salts; D009243:NAD; D005486:Flavin Mononucleotide; C023107:NADH oxidase; D009247:NADH, NADPH Oxidoreductases