Diversity of non-stoichiometric substitutions on the lipopolysaccharide of E. coli C demonstrated by electrospray ionization single quadrupole mass spectrometry

Determination of the three-dimensional structure of bacteriophage Mu(-) tail fiber and its characterization

Bacteriophage Mu is a temperate phage known to infect various species of Enterobacteria, playing a role in bacterial mutation induction and horizontal gene transfer. The phage possesses two types of tail fibers important for host recognition, which enable it to expand its range of hosts. The alternate tail fibers are formed through the action of genes 49-50 or 52-51, allowing the Mu phage to recognize different surfaces of host cells. In a previous study, we presented the X-ray crystal structure of the C-terminal lipopolysaccharide (LPS)-binding domain of gene product (gp) 49, one of the subunits comprising the Mu tail fiber. In this study, we have determined the structure of the alternative tail fiber subunit, gp52, and compared it with other tail fibers. The results revealed that Mu phage employs different structural motifs for two individual tail fibers for recognizing different hosts.

Shotgun Analysis of Rough-Type Lipopolysaccharides Using Ultraviolet Photodissociation Mass Spectrometry

Detailed structural characterization of intact rough-type lipopolysaccharides (R-LPS) was accomplished using a multi-stage mass spectrometry (MS(3)) strategy consisting of collision-induced dissociation (CID) followed by 193 ultraviolet photodissociation (UVPD) implemented on an Orbitrap Fusion mass spectrometer. Complex mixtures of R-LPS from either Escherichia coli or Salmonella enterica were directly infused into the mass spectrometer using static source nanoelectrospray ionization (nanoESI). An initial CID event performed on an R-LPS precursor produced spectra with abundant ions corresponding to the lipid A and core oligosaccharide (OS) substructures. Comparison of CID spectra of R-LPS ions with varying lipid A and core OS structures verifies that lipid A and core OS ions are consistently produced in high abundance. The resulting lipid A and core OS ions were subsequently activated by CID, high-energy collision-induced dissociation (HCD), or UVPD. For both the lipid A and core OS substructures, HCD and UVPD produced highly informative complementary spectra, with UVPD of the core OS producing an extensive array of cross-ring cleavage fragments. Successful discernment of E. coli R-LPS structures with isomeric core structures confirmed the degree to which subtle structural differences could be determined using this method.

Top-Down Strategies for the Structural Elucidation of Intact Gram-negative Bacterial Endotoxins

Re-modelling of lipopolysaccharides, which are the primary constituent of the outer cell membrane of Gram-negative bacteria, modulates pathogenesis and resistance to microbials. Reported herein is the characterization of intact Gram-negative bacterial lipooligosaccharides (LOS) via a new strategy utilizing online liquid chromatography (LC) coupled with ultraviolet photodissociation (UVPD) mass spectrometry. Compared to collision-based MS/MS methods, UVPD and UVPD/HCD promoted a greater array of cleavages within both the glycan and lipid moieties, including C-C, C-N, C-O cleavages in the acyl chains as well as glycosidic and cross-ring cleavages, thus providing the most far-reaching structural characterization of LOS. This LC-MS/MS strategy affords a robust analytical method to structurally characterize complex mixtures of bacterial endotoxins that maintains the integrity of the core oligosaccharide and lipid A domains of LOS, providing direct feedback about the cell envelope architectures and LOS modification strategies involved in resistance host innate immune defense.

Improved separation and characterization of lipopolysaccharide related compounds by reverse phase ion pairing-HPLC/electrospray ionization-quadrupole-mass spectrometry (RPIP-HPLC/ESI-Q-MS)

A new approach for the separation and inline characterization of lipopolysaccharide (LPS) related compounds has been developed. The separation was based on the difference in the number of charged phosphate and ethanolamine groups, as non-stoichiometric substituents, on the polysaccharide backbone, and was achieved with reverse phase ion-pairing chromatography (RPIP-HPLC). Tributylamine was used as an ion-pair reagent. In the conditions used in this study, tributylammonium then binds to the LPS related compounds through the negatively charged phosphate groups. This changes the hydrophobicity of the analytes at different positions and allows for separation based on both the number and position of the substituents on the analyte. The RPIP-HPLC was found to be effective for the separation of the O,N-deacylated derivative (deON) and polysaccharide portion (PS) from the LPS of Escherichia coli C strain. Post-column fluorescence derivatization (FLD), using sodium periodate and taurine, was used to detect the separated LPS related species. On the other hand, the separated species were also detected by direct infusion into the ESI-Q-MS using a volatile ammonium acetate buffer rather than the more traditional potassium phosphate buffer. The signal to noise ratio (S/N ratio) was low for the total ion chromatogram, however, high S/N ratios as well as good resolution were attained by selected ion monitoring (SIM) using m/z numbers corresponding to species with different numbers of non-stoichiometric substituents. Five species for deON and ten species for PS were clearly identified on the SIM chromatogram on the RPIP-HPLC/ESI-Q-MS. Accordingly, the present method allows for the effective separation and inline identification of the species corresponding to the diverse non-stoichiometric substitutions in LPS related compounds.