Characterization of the pH-dependent dissociation of a multimeric metalloprotein Streptomyces rubiginosus xylose isomerase by ESI FT-ICR mass spectrometry
2008
Jänis, Janne | Pasanen, Salla | Rouvinen, Juha | Vainiotalo, Pirjo
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 ~173-kDa tetrameric complex, comprised of four identical ~43-kDa subunits and eight metal cations, unequivocally identified as the Mg²⁺ 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 Mg²⁺ cations at pH [less-than or equal to]5.0, followed by step-by-step dissociation of the remaining apo-tetramer to trimers, dimers and monomers. In addition, a ~346-kDa protein octamer was detected at pH 6.9.
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