title: Glutamate dehydrogenase isoforms with N-terminal (His)6- or FLAG-tag retain their kinetic properties and cellular localization.
abstract: Glutamate dehydrogenase (GDH) is a crucial enzyme on the crossroads of amino acid and energy metabolism and it is operating in all domains of life. According to current knowledge GDH is present only in one functional isoform in most animals, including mice. In addition to this housekeeping enzyme (hGDH1 in humans), humans and apes have acquired a second isoform (hGDH2) with a distinct tissue expression profile. In the current study we have cloned both mouse and human GDH constructs containing FLAG and (His)6 small genetically-encoded tags, respectively. The hGDH1 and hGDH2 constructs containing N-terminal (His)6 tags were successfully expressed in Sf9 cells and the recombinant proteins were isolated to ≥95 % purity in a two-step procedure involving ammonium sulfate precipitation and Ni(2+)-based immobilized metal ion affinity chromatography. To explore whether the presence of the FLAG and (His)6 tags affects the cellular localization and functionality of the GDH isoforms, we studied the subcellular distribution of the expressed enzymes as well as their regulation by adenosine diphosphate monopotassium salt (ADP) and guanosine-5'-triphosphate sodium salt (GTP). Through immunoblot analysis of the mitochondrial and cytosolic fraction of the HEK cells expressing the recombinant proteins we found that neither FLAG nor (His)6 tag disturbs the mitochondrial localization of GDH. The addition of the small tags to the N-terminus of the mature mitochondrial mouse GDH1 or human hGDH1 and hGDH2 did not change the ADP activation or GTP inhibition pattern of the proteins as compared to their untagged counterparts. However, the addition of FLAG tag to the C-terminus of the mouse GDH left the recombinant protein fivefold less sensitive to ADP activation. This finding highlights the necessity of the functional characterization of recombinant proteins containing even the smallest available tags.
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark.
authors.forename: Kamilla
authors.initials: K
authors.lastname: Pajęcka
authors.forename: Camilla Wendel
authors.initials: CW
authors.lastname: Nielsen
authors.forename: Anne
authors.initials: A
authors.lastname: Hauge
authors.forename: Ioannis
authors.initials: I
authors.lastname: Zaganas
authors.forename: Lasse K
authors.initials: LK
authors.lastname: Bak
authors.forename: Arne
authors.initials: A
authors.lastname: Schousboe
authors.forename: Andreas
authors.initials: A
authors.lastname: Plaitakis
authors.forename: Helle S
authors.initials: HS
authors.lastname: Waagepetersen
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D005969:Glutamate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006639:Histidine / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C471213:His-His-His-His-His-His; D009842:Oligopeptides; D020033:Protein Isoforms; D011994:Recombinant Proteins; D006639:Histidine; D000244:Adenosine Diphosphate; D006160:Guanosine Triphosphate; C085706:FLAG peptide; D005969:Glutamate Dehydrogenase