LipidBlast (Feb 2014) currently covers 29 lipid classes across 57 different adduct and fragmentation libraries. The class designation is based on structural differences, for example lysoPC, plasmenyl-PC, plasmanyl-PC and diether-PC are considered four independent classes. New classes are updated constantly (Feb 2016).
Each of these 29 lipid classes can (potentially) ionize in negative or positive mode under different adducts such as [M+H]+, [M+Ac-H]-, [M+Cl]-, [M+Na]+ and other adduct formations. Just because the adduct is unknown to the reader, does not exclude that a certain esoteric adduct class exists. Simply many adducts may occour only under specific ionization modes (MALDI) or they were simply ignored in the past. LipidBlast does not claim nor has complete coverage of all possible adducts and ionization pathways. For each of the different lipid classes and adduct types a single small fragmentation library has been developed. The precursor ions and product ion fragmentations are consistent, but change for each of the different adduct types. Whenever an adduct type was included it was also validated, hence there are no [M+K]+ ions in LipdBlast because no experimental MS/MS spectra were found or acquired.
|Num||LipidClass||Short||Num compounds||MS/MS spectra||MS/MS LIBS|
|10||Lyso phosphatidic acids||lysoPA||80||80||1|
|25||Diacylated phosphatidylinositol monomannoside||Ac2PIM1||144||144||1|
|26||Diacylated phosphatidylinositol dimannoside||Ac2PIM2||144||144||1|
|27||Triacylated phosphatidylinositol dimannoside||Ac3PIM2||1728||1728||1|
|28||Tetraacylated phosphatidylinositol dimannoside||Ac4PIM2||20736||20736||1|
|29||Diphosphorylated hexaacyl Lipid A||LipidA-PP||15625||15625||1|
Adduct classes: [M+H]+; [M+Na]+; [M+NH4]+; [M-H]-; [M-2H](2-); [M+NH4-CO]+; [M+Na2-H]+; [M]+;
[M-H+Na]+; [M+Li]+; [M-Me]+; [M+Formate]+; [M+Acetate]
The coverage of lipid classes in LipidBlast was directly correlated to the existence of commercial standards and publications from diverse groups in the past. For example over 40 sphingolipid classes exist in LipidMaps and thousands of papers were published regarding sphingolipids (15k in Google, 5k in WOS), but most authors did not share any MS/MS spectra or simply forgot to do so or simply there was no technology to share electronic spectra. For many additional lipid classes no standard reference compounds exist or they are very expensive. One could argue that all lipid classes are equally important, depending on organism and cell compartment, so in principle any plant, bacterial, viral and animal lipid class should be covered. The reality is however that with global lipid profiling only the most 500-600 abundant lipids can be covered, and other lipid classes require complex fractionation, purification and enrichment strategies to measure them reliably in MS/MS or MSn mode.
Links and downloads:
- LipidBlast structure classes [PDF] [PPT] [SDF] [MRV] (Marvin View)
- LipidBlast additional references [PDF]
- LipidMaps structure classes and classifications [LINK]