The human gastrointestinal tract harbors a heterogeneous and complex microbial community, which plays a key role in human health. The gut microbiota controls the development of the immune system by setting systemic threshold for immune activation. Glycoconjugates, such as lipopolysaccharides, from gut bacteria have been shown to be able to elicit both systemic proinflammatory and immunomodulatory responses. This phenomenon is particularly intriguing considering that the immune system is charged with the task to distinguish the beneficial microbes from the pathogens, even if the commensal bacteria have molecular patterns resembling those of the pathogenic counterparts. Therefore, the importance of the chemical structure of these macromolecules in fine tuning this delicate equilibrium is beyond question. This review offers an overview of the current understanding of chemical peculiarities of the lipopolysaccharides isolated from the gut microbiota, and their relationships to their biological activity in terms of immune system maturation and development.

innate immunity, Structural characterization, gut immunity, gut microbiota, TLR4/MD-2

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CCCCCCCCCCCCCCCC(=O)OC(CCCCCCCCCCC)CC(=O)N[C@H]1[C@@H](OP(=O)(O)OP(=O)(O)OCCN)O[C@H](CO[C@@H]2O[C@H](CO)[C@@H](OP(=O)(O)O[C@H]3OC[C@H](N)[C@H](O)[C@H]3O)[C@H](OC(=O)CC(CCCCCCCCCCC)OC(=O)CCCCCCCCCCCCC)[C@H]2NC(=O)CC(CCCCCCCCCCC)OC(=O)CCCCCCCCCCC)[C@@H](O)[C@@H]1OC(=O)CC(O)CCCCCCCCCCC

2290.989 g/mol (C₁₁₇H₂₂₃N₄O₃₂P₃)

This paper describes the structure of neutral exopolysaccharide (EPS) produced by Lactobacillus johnsonii 142, strain of the lactic acid bacteria isolated from the intestine of mice with experimentally induced inflammatory bowel disease (IBD). Sugar and methylation analyses along with (1)H and (13)C NMR spectroscopy, including two-dimensional (1)H,(1)H COSY, TOCSY, NOESY, and (1)H,(13)C HSQC experiments revealed that the repeating unit of the EPS is a pentasaccharide: →3)-α-D-Galp-(1→3)-β-D-Glcp-(1→5)-β-D-Galf-(1→3)-α-D-Galp-(1→3)-α-D-Galp-(1→ The rabbit antiserum raised against whole cells of L. johnsonii 142 reacted with homologous EPS, and cross-reacted with exopolysaccharide from Lactobacillus animalis/murinus 148 isolated also from mice with IBD, but not reacted with EPS of L. johnsonii 151 from healthy mice.

Lactic acid bacteria, exopolysaccharide, Crohn disease, Lactobacillus johnsonii, inflammatory bowel disease, probiotic

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,3,5,3	aDGalp	99.2	67.6	74.11	65.68	71.0	61.4
3,3,5	bDGlcp	102.1	72.5	82.2	70.2	75.6	61.1
3,3	bDGalf	109.4	81.9	76.6	81.8	77.8	61.8
3	aDGalp	95.6	67.57	77.7	69.7	71.1	61.4
	aDGalp	95.2	67.1	74.6	66.1	71.25	61.4


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,3,5,3	aDGalp	5.44	3.98	4.06	4.29	4.27	3.81
3,3,5	bDGlcp	4.66	3.43	3.69	3.65	3.47	3.75-3.89
3,3	bDGalf	5.20	4.20	4.27	4.18	4.07	3.77
3	aDGalp	5.19	3.99	4.02	4.16	4.22	3.82
	aDGalp	5.23	4.04	4.11	4.27	4.21	3.74


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,3,5,3	aDGalp	99.2/5.44	67.6/3.98	74.11/4.06	65.68/4.29	71.0/4.27	61.4/3.81
3,3,5	bDGlcp	102.1/4.66	72.5/3.43	82.2/3.69	70.2/3.65	75.6/3.47	61.1/3.75-3.89
3,3	bDGalf	109.4/5.20	81.9/4.20	76.6/4.27	81.8/4.18	77.8/4.07	61.8/3.77
3	aDGalp	95.6/5.19	67.57/3.99	77.7/4.02	69.7/4.16	71.1/4.22	61.4/3.82
	aDGalp	95.2/5.23	67.1/4.04	74.6/4.11	66.1/4.27	71.25/4.21	61.4/3.74

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

*O[C@H]1[C@@H](O)[C@@H](CO)O[C@H](O[C@@H]2[C@@H](O)[C@H](O[C@H](CO)[C@@H]3O[C@@H](O[C@H]4[C@@H](O)[C@@H](CO)O[C@H](O[C@@H]5[C@@H](O)[C@@H](*)O[C@H](CO)[C@@H]5O)[C@@H]4O)[C@H](O)[C@H]3O)O[C@H](CO)[C@H]2O)[C@@H]1O

810.705 g/mol (C₃₀H₅₀R₂O₂₅, R = next and previous repeats, not counted in mol weight)