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The role of mobile protons in negative ion CID of oligosaccharides.

ABSTRACT: Carbohydrates of all classes consist of glycoform mixtures built on common core units. Determination of compositions and structures of such mixtures relies heavily on tandem mass spectrometric data. Analysis of native glycans is often necessary for samples available in very low quantities and for sulfated glycan classes. Negative tandem mass spectrometry (MS) provides useful product ion profiles for neutral oligosaccharides and is preferred for acidic classes. In previous work from this laboratory, site-specific influences of sialylation on product ion profiles in the negative mode were elucidated. The present results show how the interplay of two other acidic groups, uronic acids and sulfates, determines product ion patterns for chondroitin sulfate oligosaccharides. Unsulfated chondroitin oligosaccharides dissociate to form C-type ions almost exclusively. Chondroitin sulfate oligosaccharides produce abundant B- and Y-type ions from glycosidic bond cleavage with C- and Z-types in low abundances. These observations are explained in terms of competing proton transfer reactions that occur during the collisional heating process. Mechanisms for product ion formation are proposed based on tandem mass spectra and the abundances of product ions as a function of collision energy.

SUBMITTER: Zaia J

PROVIDER: S-EPMC1964798 | biostudies-literature | 2007 May

REPOSITORIES: biostudies-literature

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The role of mobile protons in negative ion CID of oligosaccharides.

Zaia Joseph J Miller May Joy C MJ Seymour Jennifer L JL Costello Catherine E CE

Journal of the American Society for Mass Spectrometry 20070323 5

Carbohydrates of all classes consist of glycoform mixtures built on common core units. Determination of compositions and structures of such mixtures relies heavily on tandem mass spectrometric data. Analysis of native glycans is often necessary for samples available in very low quantities and for sulfated glycan classes. Negative tandem mass spectrometry (MS) provides useful product ion profiles for neutral oligosaccharides and is preferred for acidic classes. In previous work from this laborato ...[more]

PMID: 17383193

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Project description:Most hyphenated analytical approaches that rely on liquid chromatography-MS require relatively long separation times, produce incomplete resolution of oligosaccharide mixtures, use eluents that are incompatible with electrospray ionization, or require oligosaccharide derivatization. Here we demonstrate the analysis of heparin oligosaccharides, including disaccharides, ultralow molecular weight heparin, and a low molecular weight heparin, using a novel electrokinetic pump-based CE-MS coupling eletrospray ion source. Reverse polarity CE separation and negative-mode electrospray ionization were optimized using a volatile methanolic ammonium acetate electrolyte and sheath fluid. The online CE hyphenated negative-ion electrospray ionization MS on an LTQ Orbitrap mass spectrometer was useful in disaccharide compositional analysis and bottom-up and top-down analysis of low molecular weight heparin. The application of this CE-MS method to ultralow molecular heparin suggests that a charge state distribution and the low level of sulfate group loss that is achieved make this method useful for online tandem MS analysis of heparins. Graphical abstract Most hyphenated analytical approaches that rely on liquid chromatography-MS require relatively long separation times, produce incomplete resolution of oligosaccharide mixtures, use eluents that are incompatible with electrospray ionization, or require oligosaccharide derivatization. Here we demonstrate the analysis of heparin oligosaccharides, including disaccharides, ultralow molecular weight heparin, and a low molecular weight heparin, using a novel electrokinetic pump-based CE-MS coupling eletrospray ion source. Reverse polarity CE separation and negative-mode electrospray ionization were optimized using a volatile methanolic ammonium acetate electrolyte and sheath fluid. The online CE hyphenated negative-ion electrospray ionization MS on an LTQ Orbitrap mass spectrometer was useful in disaccharide compositional analysis and bottom-up and top-down analysis of low molecular weight heparin. The application of this CE-MS method to ultralow molecular heparin suggests that a charge state distribution and the low level of sulfate group loss that is achieved make this method useful for online tandem MS analysis of heparins.

Project description:Ion channels, which are found in every biological cell, regulate the concentration of electrolytes, and are responsible for multiple biological functions, including in particular the propagation of nerve impulses. The channels with the latter function are gated (opened) by a voltage signal, which allows Na(+) into the cell and K(+) out. These channels have several positively charged amino acids on a transmembrane domain of their voltage sensor, and it is generally considered, based primarily on two lines of experimental evidence, that these charges move with respect to the membrane to open the channel. At least three forms of motion, with greatly differing extents and mechanisms of motion, have been proposed. There is a "gating current", a capacitative current preceding the channel opening, that corresponds to several charges (for one class of channel typically 12-13) crossing the membrane field, which may not require protein physically crossing a large fraction of the membrane. The coupling to the opening of the channel would in these models depend on the motion. The conduction itself is usually assumed to require the "gate" of the channel to be pulled apart to allow ions to enter as a section of the protein partially crosses the membrane, and a selectivity filter at the opposite end of the channel determines the ion which is allowed to pass through. We will here primarily consider K(+) channels, although Na(+) channels are similar. We propose that the mechanism of gating differs from that which is generally accepted, in that the positively charged residues need not move (there may be some motion, but not as gating current). Instead, protons may constitute the gating current, causing the gate to open; opening consists of only increasing the diameter at the gate from approximately 6 Å to approximately 12 Å. We propose in addition that the gate oscillates rather than simply opens, and the ion experiences a barrier to its motion across the channel that is tuned by the water present within the channel. Our own quantum calculations as well as numerous experiments of others are interpreted in terms of this hypothesis. It is also shown that the evidence that supports the motion of the sensor as the gating current can also be consistent with the hypothesis we present.

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The role of mobile protons in negative ion CID of oligosaccharides.

Publications

The role of mobile protons in negative ion CID of oligosaccharides.

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