title: Mass spectrometric study of gas-phase ions of acid β-glucosidase (Cerezyme) and iminosugar pharmacological chaperones.
abstract: The effect on the conformations and stability of gas-phase ions of Cerezyme, a glycoprotein, when bound to three small-molecule chaperones has been studied using intact ESI MS, collision cross section and MS/MS measurements. To distinguish between the peaks from apo and small-molecule complex ions, Cerezyme is deglycosylated (dg-Cer). ESI MS of dg-Cer reveals that glycosylation accounts for 8.5% of the molecular weight. When excess chaperone, either covalent (2FGF) or noncovalent (A and B iminosugars), is added to solutions of dg-Cer, mass spectra show peaks from 1:1 chaperone-enzyme complexes as well as free enzyme. On average, ions of the apoenzyme have 1.6 times higher cross sections when activated in the source region of the mass spectrometer. For a given charge state, ions of complexes of 2FGF and B have about 30% and 8.4% lower cross sections, respectively, compared to the apoenzyme. Thus, binding the chaperones causes the gas-phase protein to adopt more compact conformations. The noncovalent complex ions dissociate by the loss of charged chaperones. In the gas phase, the relative stability of dg-Cer with B is higher than that with the A, whereas in solution A binds enzyme more strongly than B. Nevertheless, the disagreement is explained based on the greater number of contacts between the B and dg-Cer than the A and dg-Cer (13 vs. 8), indicating the importance of noncovalent interactions within the protein-chaperone complex in the absence of solvent. Findings in this work suggest a hypothesis towards predicting a consistent correlation between gas-phase properties to solution binding properties.
authors.affiliation: Department of Chemistry, University of British Columbia (UBC), 2036 Mail Mall, Vancouver, BC, V6T 1Z1, Canada; Astbury Centre for Structural Molecular Biology (ACSMB), University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK.
authors.forename: Khadijeh
authors.initials: K
authors.lastname: Rajabi
mesh_terms: D000595:Amino Acid Sequence; D003847:Deoxyglucose / Q000031:analogs & derivatives; D005740:Gases / Q000737:chemistry; D005962:Glucosylceramidase / Q000737:chemistry* / Q000378:metabolism; D006031:Glycosylation; D050111:Imino Sugars / Q000737:chemistry* / Q000378:metabolism; D007477:Ions / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D053719:Tandem Mass Spectrometry
chemical_list: D005740:Gases; D050111:Imino Sugars; D007477:Ions; C041022:2-deoxy-2-fluoroglucopyranosyl fluoride; D003847:Deoxyglucose; D005962:Glucosylceramidase; C090568:imiglucerase
keywords: (non)-covalent glycoprotein complex; deglycosylated Cerezyme cross section; intact glycoprotein ESI MS; triple-quadrupole MS; β-glucocerebrosidase