Structural characterization of glycerophospholipids by combinations of ozone- and collision-induced dissociation mass spectrometry: the next step towards "top-down" lipidomics.
The complete structural elucidation of complex lipids, including glycerophospholipids, using only mass spectrometry represents a major challenge to contemporary analytical technologies. Here, we demonstrate that product ions arising from the collision-induced dissociation (CID) of the [M + Na](+) adduct ions of phospholipids can be isolated and subjected to subsequent gas-phase ozonolysis - known as ozone-induced dissociation (OzID) - in a linear ion-trap mass spectrometer. The resulting CID/OzID experiment yields abundant product ions that are characteristic of the acyl substitution on the glycerol backbone (i.e., sn-position). This approach is shown to differentiate sn-positional isomers, such as the regioisomeric phosphatidylcholine pair of PC 16:0/18:1 and PC 18:1/16:0. Importantly, CID/OzID provides a sensitive diagnostic for the existence of an isomeric mixture in a given sample. This is of very high value for the analysis of tissue extracts since CID/OzID analyses can reveal changes in the relative abundance of isomeric constituents even within different tissues from the same animal. Finally, we demonstrate the ability to assign carbon-carbon double bond positions to individual acyl chains at specific backbone positions by adding subsequent CID and/or OzID steps to the workflow and that this can be achieved in a single step using a hybrid triple quadrupole-linear ion trap mass spectrometer. This unique approach represents the most complete and specific structural analysis of lipids by mass spectrometry demonstrated to date and is a significant step towards comprehensive top-down lipidomics.
ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, School of Chemistry, University of Wollongong, NSW, Australia. blanksby@uow.edu.au toddm@uow.edu.au.
Huong T
HT
Pham
Alan T
AT
Maccarone
Michael C
MC
Thomas
J Larry
JL
Campbell
Todd W
TW
Mitchell
Stephen J
SJ
Blanksby
D000818:Animals; D002417:Cattle; D020404:Glycerophospholipids / Q000032:analysis* / Q000737:chemistry*; D008055:Lipids / Q000032:analysis / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods*; D010126:Ozone / Q000737:chemistry*
D020404:Glycerophospholipids; D008055:Lipids; D010126:Ozone