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Structural elucidation of diglycosyl diacylglycerol and monoglycosyl diacylglycerol from Streptococcus pneumoniae by multiple-stage linear ion-trap mass spectrometry with electrospray ionization.

ABSTRACT: The cell wall of the pathogenic bacterium Streptococcus pneumoniae contains glucopyranosyl diacylglycerol (GlcDAG) and galactoglucopyranosyldiacylglycerol (GalGlcDAG). The specific GlcDAG consisting of vaccenic acid substituent at sn-2 was recently identified as another glycolipid antigen family recognized by invariant natural killer T-cells. Here, we describe a linear ion-trap multiple-stage (MS(n) ) mass spectrometric approach towards structural analysis of GalGlcDAG and GlcDAG. Structural information derived from MS(n) (n?=?2, 3) on the [M?+?Li](+) adduct ions desorbed by electrospray ionization affords identification of the fatty acid substituents, assignment of the fatty acyl groups on the glycerol backbone, as well as the location of double bond along the fatty acyl chain. The identification of the fatty acyl groups and determination of their regio-specificity were confirmed by MS(n) (n?=?2, 3) on the [M?+?NH(4) ](+) ions. We establish the structures of GalGlcDAG and GlcDAG isolated from S. pneumoniae, in which the major species consists of a 16:1- or 18:1-fatty acid substituent mainly at sn-2, and the double bond of the fatty acid is located at ?-7 (n-7). More than one isomers were found for each mass in the family. This mass spectrometric approach provides a simple method to achieve structure identification of this important lipid family that would be very difficult to define using the traditional method.

SUBMITTER: Tatituri RV

PROVIDER: S-EPMC3712276 | biostudies-literature | 2012 Jan

REPOSITORIES: biostudies-literature

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Structural elucidation of diglycosyl diacylglycerol and monoglycosyl diacylglycerol from Streptococcus pneumoniae by multiple-stage linear ion-trap mass spectrometry with electrospray ionization.

Tatituri Raju Venkata Veera RV Brenner Michael B MB Turk John J Hsu Fong-Fu FF

Journal of mass spectrometry : JMS 20120101 1

The cell wall of the pathogenic bacterium Streptococcus pneumoniae contains glucopyranosyl diacylglycerol (GlcDAG) and galactoglucopyranosyldiacylglycerol (GalGlcDAG). The specific GlcDAG consisting of vaccenic acid substituent at sn-2 was recently identified as another glycolipid antigen family recognized by invariant natural killer T-cells. Here, we describe a linear ion-trap multiple-stage (MS(n) ) mass spectrometric approach towards structural analysis of GalGlcDAG and GlcDAG. Structural inf ...[more]

PMID: 22282097

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Project description:Linear ion-trap multiple-stage mass spectrometric approach (MS(n)) towards nearly complete structural elucidation of triacylglycerol (TAG) including (1) assignment the fatty acid substituents on the glycerol backbone and (2) location of the double bond(s) on the unsaturated fatty acyl groups is reported. The characterization is established by the findings that MS(2) on the [M + Li](+) ions of TAG yields more abundant ions reflecting losses of the outer fatty acid substituents either as free acids (i.e., [M + Li - R(1)CO(2)H](+) and [M + Li - R(3)CO(2)H](+) ions) or as lithium salts (i.e., [M + Li - R(1)CO(2)Li](+) and [M + Li - R(3)CO(2)Li](+) ions) than the ions reflecting the similar losses of the inner fatty acid substituent (i.e., [M + Li - R(2)CO(2)Li](+) and [M + Li - R(2)CO(2)Li](+) ions). Further dissociation (MS(3) of [M + Li - R(n)CO(2)H](+) (n = 1, 2, or 3) gives rise to the ion series locating the double bonds along the fatty acid chain. These ions arise from charge-remote fragmentations involving beta-cleavage with gamma-H shift, analogous to those seen for the unsaturated long-chain fatty acids characterized as initiated ions. Significant differences in abundances in the ion pairs reflecting the additional losses of the fatty acid moieties, respectively, were also seen in the MS(3) spectra of the [M + Li - R(n)CO(2)H](+) and [M + Li - R(n)CO(2)Li](+) ions, leading to confirmation of the fatty acid substituents on the glycerol backbone. MS(n) on the [M + Na](+) and [M + NH(4)](+) adduct ions also affords location of fatty acid substituents on the glycerol backbone, but not the position of the double bond(s) along the fatty acid chain. Unique ions from internal losses of the glycerol residues were seen in the MS(3) spectra of [M + Alk - R(n)CO(2)H](+) (n = 1, 2, 3) and of [M + Alk - R(n)CO(2)Alk](+) (Alk = Li, Na, NH(4); n = 1, 3). They are signature ions for glycerides and the pathways leading to their formation may involve rearrangements.

Dataset Information

Structural elucidation of diglycosyl diacylglycerol and monoglycosyl diacylglycerol from Streptococcus pneumoniae by multiple-stage linear ion-trap mass spectrometry with electrospray ionization.

Publications

Structural elucidation of diglycosyl diacylglycerol and monoglycosyl diacylglycerol from Streptococcus pneumoniae by multiple-stage linear ion-trap mass spectrometry with electrospray ionization.

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