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. Author manuscript; available in PMC: 2014 Apr 11.
Published in final edited form as: Innate Immun. 2013 Jun 28;20(3):269–282. doi: 10.1177/1753425913490534

Table 1.

Temperature dependence of lipid A structures in E. coli lpxL MLK217 determined by MALDI-MSn.

MS species Mr obs. (exact) Mr calc. (exact) MSn analysis Lipid A structurea (acyl group composition and positions) Temperature (°C)
30 37 42
Pentaacyl lipid A
MPLA 5 1534.8 1535.1 MS6 4×14:0(3-OH)[2′, 3′, 2, 3], 14:0 [3′-O], P +++ +++ ++
MPLA 5 1560.8 1561.1 MS6 4×14:0(3-OH)[2′, 3′, 2, 3], 16:1 [2′-O], P + +++ —
MPLA 5 1562.8 1563.1 MS6 4×14:0(3-OH)[2′, 3′, 2, 3], 16:0 [2-O], P + — +++
MPLA 5 1542.8 1543.1 MS5 4×14:0(3-OH)[2′, 2, 3′, 3], 16:1 [2′-O], P, –H2O — ++ —
Hexaacyl lipid A
MPLA 6 1770.8b 1771.4 MS7 4×14:0(3-OH)[2′, 3′, 2, 3], 14:0 [3′-O], 16:1 [2′-O], P ++ +++ —
MPLA 6 1773.0 1773.4 MS6 4×14:0(3-OH)[2′, 3′, 2, 3], 14:0 [3′-O], 16:0 [2-O], P — — +
MPLA 6 1742.8c 1743.3 MS6 4×14:0(3-OH)[2′, 3′, 2, 3], 12:0 [3’-O], 16:1 [2′-O], P; 4×14:0(3-OH)[2′, 3′, 2, 3], 14:0 [3′-O], 14:1 [2′-O], P (mix) (+) + —
Tetraacyl lipid A
MPLA 4 1324.7 1324.9 MS5 4×14:0(3-OH)[2′, 3′, 2, 3], P +++ +++ +++
MPLA 4 1334.7 1334.9 MS5 3×14:0(3-OH)[2′, 2, 3], 16:1 [2′-O], P — ++ —
MPLA 4 1336.7 1336.9 MS5 3×14:0(3-OH)[2′, 2, 3], 16:0 [2-O], P — — +
a

Position of acyl group on the disaccharide lipid backbone is indicated for primary 3-hydroxyacyl fatty acids [n:0(3-OH)] as 2′ (N-linked), and 3′ (O-linked) when located on the distal glucosamine, and as 2 (N-linked), and 3 (O-linked) when located on the reducing end of the proximal glucosamine. Positions for observed secondary acyl groups [n:0 or n:1] are indicated as [3′-O], [2-O], and [2′-O]. Secondary acyl groups are connected to the 3-hydroxy group of the corresponding primary fatty acid.

b

Previously characterized by McLendon et al.7

c

Lipid A species appear as isomer mixtures displaying different fatty acid positioning on the disaccharide lipid backbone (compositions are indicated). If no mixture is indicated, the lipid A species were observed as single isoform. All masses reported are monoisotopic masses M. Lipid A species were observed in negative ionization mode with their deprotonated molecular ion, [M-H]−, and were confirmed by MSn fragmentation on a vMALDI MSn LIT instrument as annotated.