title: Characterization of the pH-dependent dissociation of a multimeric metalloprotein Streptomyces rubiginosus xylose isomerase by ESI FT-ICR mass spectrometry.
abstract: We report an analysis of the pH-dependent dissociation of a multimeric metalloprotein, xylose isomerase from Streptomyces rubiginosus (XI), by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Xylose isomerases are industrially significant enzymes that catalyze interconversion of aldose and ketose sugars. XI is biologically active as a approximately 173-kDa tetrameric complex, comprised of four identical approximately 43-kDa subunits and eight metal cations, unequivocally identified as the Mg(2+) cations in this work. ESI FT-ICR mass spectra of XI measured in the pH range of 3.0-6.9 indicated that the dissociation of the intact holo-tetramer is initiated by the loss of all eight Mg(2+) cations at pH <or=5.0, followed by step-by-step dissociation of the remaining apo-tetramer to trimers, dimers and monomers. In addition, a approximately 346-kDa protein octamer was detected at pH 6.9.
authors.affiliation: Department of Chemistry, University of Joensuu, Joensuu, Finland. janne.janis@joensuu.fi
authors.forename: Janne
authors.initials: J
authors.lastname: Jänis
authors.forename: Salla
authors.initials: S
authors.lastname: Pasanen
authors.forename: Juha
authors.initials: J
authors.lastname: Rouvinen
authors.forename: Pirjo
authors.initials: P
authors.lastname: Vainiotalo
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D017357:Cyclotrons; D005583:Fourier Analysis; D006863:Hydrogen-Ion Concentration; D008667:Metalloproteins / Q000737:chemistry*; D011487:Protein Conformation; D011489:Protein Denaturation; D021241:Spectrometry, Mass, Electrospray Ionization; D013302:Streptomyces / Q000737:chemistry*
chemical_list: D002412:Cations; D008667:Metalloproteins; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase