Lipomannan (LM) and lipoarabinomannan (LAM) are major glycolipids present in the mycobacterial cell wall that are able to modulate the host immune response. In this study, we have undertaken the structural determination of these important modulins in Mycobacterium chelonae, a fast growing pathogenic mycobacterial species. One-dimensional and two-dimensional NMR spectra were used to demonstrate that LM and LAM from M. chelonae, designated CheLM and CheLAM, respectively, possess structures that differ from the ones reported earlier in other mycobacterial species. Analysis by gas chromatography/mass spectrometry of the phosphatidyl-myo-inositol anchor, which is thought to play a role in the biological functions of these lipoglycans, pointed to a high degree of heterogeneity based on numerous combinations of acyl groups on the C-1 and C-2 positions of the glycerol moiety. Characterization of the mannan core of CheLM and CheLAM revealed the presence of novel α1,3-mannopyranosyl side chains. This motif, which reacted specifically with the lectin from Galanthus nivalis, was found to be unique among a panel of nine mycobacterial species. Then, CheLM and CheLAM were found to be devoid of both the mannooligosaccharide cap present in Mycobacterium tuberculosis and the inositol phosphate cap present in Mycobacterium smegmatis and other fast growing species. Tumor necrosis factor-alpha and interleukin-8 production were assessed from human macrophages with LAM preparations from different species. Our results suggest that the inositol phosphate capping may represent the major cytokine-inducing component of LAMs. This work not only underlines the diversity of LAM structures among various mycobacterial species but also provides new structures that could be useful to dissect the structure-function relationships of these complex molecules.

lipopolysaccharides, antigens, cell wall, structural studies, Mycobacterium, glycolipid, immune response, lipoarabinomannan, tumor necrosis factor, CD1, interleukin-8, lectins, Mycobacterium chelonae

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
	aDManp	100.7	70.97	72.0	67.0	?	?


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
	aDManp	4.71	3.68	3.56	3.52	?	?


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
	aDManp	100.7/4.71	70.97/3.68	72.0/3.56	67.0/3.52	?/?	?/?

The spectrum also has 2 signals at unknown positions (not plotted).

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

*OC[C@H]1O[C@H](*)[C@@H](O)[C@@H](O)[C@@H]1O

162.141 g/mol (C₆H₁₀R₂O₅, R = next and previous repeats, not counted in mol weight)