title: The physicochemical properties of membranes correlate with the NADPH oxidase activity.
abstract: Phagocytes kill ingested microbes by exposure to high concentrations of toxic reactive species generated by NADPH-oxidases. This membrane-bound electron-transferring enzyme is tightly regulated by cellular signaling cascades. So far, molecular and biophysical studies of the NADPH-oxidase were performed over limited temperature ranges, which weaken our understanding of immune response or inflammatory events. In this work, we have inspected the influence of temperature and lipid membrane properties on the NADPH-oxidase activity using a system free of cell complexity.
  
  
  
  We have extended the experimental conditions of the accepted model for NADPH-oxidase activity, the so-called cell-free assay, to a large temperature range (10-40°C) using different membrane compositions (subcellular compartments or liposomes).
  
  
  
  A remarkable increase of superoxide production rate was observed with rising temperature. Synchrotron radiation circular dichroism data showed that this is not correlated with protein secondary structure changes. When lipid bilayers are in fluid phase, Arrhenius plots of the oxidase activity showed linear relationships with small activation energy (Ea), while when in solid phase, high Ea was found. The sterol content modulates kinetic and thermodynamic parameters.
  
  
  
  High temperature promotes the rate of superoxide production. The key element of this enhancement is related to membrane properties such as thickness and viscosity and not to protein structural changes. Membrane viscosity that can be driven by sterols is a paramount parameter of Ea of NADPH oxidase activity. The membrane bilayer state modulated by its sterol content may be considered locally as an enzyme regulator. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.
authors.affiliation: Laboratoire de Chimie Physique UMR 8000, Univ. Paris-Sud, CNRS, Université Paris Saclay, 91405 Orsay Cedex, France.
authors.forename: Hager
authors.initials: H
authors.lastname: Souabni
authors.affiliation: Synchrotron SOLEIL, Campus Paris-Saclay, 91192 Gif-sur-Yvette Cedex, France.
authors.forename: Frank
authors.initials: F
authors.lastname: Wien
authors.affiliation: Laboratoire de Chimie Physique UMR 8000, Univ. Paris-Sud, CNRS, Université Paris Saclay, 91405 Orsay Cedex, France.
authors.forename: Tania
authors.initials: T
authors.lastname: Bizouarn
authors.affiliation: Laboratoire de Chimie Physique UMR 8000, Univ. Paris-Sud, CNRS, Université Paris Saclay, 91405 Orsay Cedex, France.
authors.forename: Chantal
authors.initials: C
authors.lastname: Houée-Levin
authors.affiliation: Synchrotron SOLEIL, Campus Paris-Saclay, 91192 Gif-sur-Yvette Cedex, France.
authors.forename: Matthieu
authors.initials: M
authors.lastname: Réfrégiers
authors.affiliation: Laboratoire de Chimie Physique UMR 8000, Univ. Paris-Sud, CNRS, Université Paris Saclay, 91405 Orsay Cedex, France. Electronic address: laura.baciou@u-psud.fr.
authors.forename: Laura
authors.initials: L
authors.lastname: Baciou
mesh_terms: D016718:Arachidonic Acid / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D055598:Chemical Phenomena; D002942:Circular Dichroism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D008051:Lipid Bilayers / Q000378:metabolism; D008954:Models, Biological; D019255:NADPH Oxidases / Q000378:metabolism*; D010843:Pichia; D055550:Protein Stability; D011510:Proteolipids / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013261:Sterols / Q000378:metabolism; D017356:Synchrotrons; D013696:Temperature
chemical_list: D008051:Lipid Bilayers; D011510:Proteolipids; D011994:Recombinant Proteins; D013261:Sterols; C020485:proteoliposomes; D016718:Arachidonic Acid; D019255:NADPH Oxidases
keywords: Lipids; Membrane proteins; NADPH oxidase (Nox); Phase transition; Recombinant cell free assay; SRCD; Sterols; Temperature dependence