Journal
JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY
Volume 18, Issue 6, Pages 1080-1092Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.jasms.2007.03.008
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Funding
- NCRR NIH HHS [S10 RR017262, 1S10RR17262-01] Funding Source: Medline
- NIAID NIH HHS [U54 AI057141-010005, U54 AI057141, 1U54AI57141-01] Funding Source: Medline
- NIEHS NIH HHS [P30ES07033, P30 ES007033] Funding Source: Medline
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The structural characterization of environmentally-regulated lipid A derived from Francisella tularensis subspecies novicida (Fn) U112 is described using negative electrospray ionization with a linear ion trap Fourier transform ion cyclotron resonance (IT-FT-ICR) hybrid mass spectrometer. The results indicate that a unique profile of lipid A molecular structures are synthesized in response to Fn growth at 25 degrees C versus 37 degrees C. Molecular species were found to be tetra-acylated, sharing a conserved glucosamine disaccharide backbone, a galactosamine-1-phosphate linked to the reducing glucosamine, and multiple O- and N-linked fatty acyl groups. Deprotonated molecules were interrogated by MSn scanning techniques at both high and nominal mass resolution and were found to be complex heterogeneous mixtures where structures differed based on the positions and identities of the O- and N-linked fatty acyl substituents. For the dominant ion series, which consisted of five peaks, 30 unique lipid A structures were identified. Estimates for the relative abundance of each structure were derived from MS relative abundance ratios and fragment ion ratios from comparable dissociation pathways from MS2 through MS4 experiments. The results suggest a remodeling pathway in which the amide linked fatty acid of the reducing glucosamine favors a 3-hydroxyhexadecanoic acid substituent for growth conditions at 25 degrees C versus a 3-hydroxyoctadecanoic acid substituent for growth conditions at 37 degrees C.
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