Structural Analysis of an Unusual BioactiveN-Acylated Lipo-Oligosaccharide LOS-IV inMycobacterium marinum

Abstract

Although lipo-oligosaccharides (LOSs) are recognized as major parietal components in many mycobacterial species, their involvement in the host-pathogen interactions have been scarcely documented. In particular, the biological implications arising from the high degree of structural species-specificity of these glycolipids remain largely unknown. Growing recognition of the Mycobacterium marinum-Danio rerio as a specific host-pathogen model devoted to the study of the physiopathology of mycobacterial infections prompted us to elucidate the structure-to-function relationships of the elusive end-product, LOS-IV, of the LOS biosynthetic pathway in M. marinum. Combination of physicochemical and molecular modeling methods established that LOS-IV resulted from the differential transfer on the caryophyllose-containing LOS-III of a family of very unusual N-acylated monosaccharides, naturally present as different diastereoisomers. In agreement with the partial loss of pathogenecity previously reported in a LOS-IV-deficient M. marinum mutant, we demonstrated that this terminal monosaccharide conferred to LOS-IV important biological functions, including macrophage activating properties.

Unexpected Link between Lipooligosaccharide Biosynthesis and Surface Protein Release in Mycobacterium marinum

“…In contrast to these in vivo experiments, recent in vitro infections of murine macrophage cell lines with different M. marinum LOS mutants demonstrated impaired cell-entry efficiency (15). Also, the addition of purified LOS-IV to macrophages resulted in an altered pro-inflammatory response (19,32). However, from our studies it seems that LOS-IV deficiency actually results in a more pronounced infection, suggesting a different mechanism in the context of zebrafish embryos.…”

“…The addition of xylose together with one or two molecules of the highly unusual sugar caryophyllose (19) produces LOS-II and LOS-III, respectively. The molecule added to produce LOS-IV has been characterized as a heterogenic group of mainly one acidic form of an N-acylated 4-amino-4,6-dideoxy-Galp residue (resulting in LOS-IVc) with a minor population of two neutral forms (LOS-IVa and -b) (32). The biosynthetic pathway for LOS and the genes involved is largely unknown.…”

Acyltransferases in Bacteria

“…LOS comprises a third type of mycobacterial glycolipids with an acylated trehalose section which is further glycosylated in a complex manner (174,175). In M. marinum, there are four LOS subtypes (I to IV) that differ in the glycan moieties but share a similar acylation pattern, with two 2,4-dimethylhexadecanoate residues linked to positions C4 and C2 of the terminal and internal glucose residue, respectively.…”

Fatty Acyl Chains of Mycobacterium marinum Lipooligosaccharides

“…Furthermore, this result was supported by the finding that a M. marinum isolate (Mma7) unable to produce LOS-IV (19) failed to show signs of infection in adult zebrafish (20). As a first step to address the role of LOSs in M. marinum virulence, we characterized the glycosidic structures of LOS-I to LOS-IV (19,21). Structural analyses demonstrated that LOS-I, -II, -III, and -IV share a common glycan core consisting of the acylated trehalose substituted by two ␤-D-Glcp residues and one 3-O-methylated ␣-L-Rhap.…”