2 research outputs found
Disruption of Mycobacterial AftB Results in Complete Loss of Terminal β(1 → 2) Arabinofuranose Residues of Lipoarabinomannan
Lipoarabinomannan
(LAM) and arabinogalactan (AG) are the two major
mycobacterial cell wall (lipo)polysaccharides, which contain a structurally
similar arabinan domain that is highly branched and assembled in a
stepwise fashion by variety of arabinofuranosyltransferases (Ara<i>f</i>T). In addition to playing an essential role in mycobacterial
physiology, LAM and its biochemical precursor lipomannan possess potent
immunomodulatory activities that affect the host immune response.
In the search of additional mycobacterial Ara<i>f</i>Ts
that participate in the synthesis of the arabinan segment of LAM,
we disrupted <i>aftB</i> (<i>MSMEG_6400</i>) in <i>Mycobacterium smegmatis</i>. The deletion of chromosomal <i>aftB</i> locus could only be achieved in the presence of a rescue
plasmid carrying a functional copy of <i>aftB</i>, strongly
suggesting that it is essential for the viability of <i>M. smegmatis</i>. Isolation and detailed structural characterization of a LAM molecule
derived from the conditional mutant deficient in AftB revealed the
absence of terminal β(1 → 2)-linked arabinofuranosyl
residues. Furthermore, we demonstrated that truncated LAM displays
proinflammatory activity, which is due to its ability to activate
Toll-like receptor 2. All together, our results indicate that AftB
is an essential mycobacterial Ara<i>f</i>T that plays a
role in the synthesis of the arabinan domain of LAM
The role of hydrophobicity in tuberculosis evolution and pathogenicity
The evolution of tubercle bacilli parallels a route from environmental Mycobacterium kansasii, through intermediate "Mycobacterium canettii", to the modern Mycobacterium tuberculosis complex. Cell envelope outer membrane lipids change systematically from hydrophilic lipooligosaccharides and phenolic glycolipids to hydrophobic phthiocerol dimycocerosates, di- and pentaacyl trehaloses and sulfoglycolipids. Such lipid changes point to a hydrophobic phenotype for M. tuberculosis sensu stricto. Using Congo Red staining and hexadecane-aqueous buffer partitioning, the hydrophobicity of rough morphology M. tuberculosis and Mycobacterium bovis strains was greater than smooth "M. canettii" and M. kansasii. Killed mycobacteria maintained differential hydrophobicity but defatted cells were similar, indicating that outer membrane lipids govern overall hydrophobicity. A rough M. tuberculosis H37Rv ΔpapA1 sulfoglycolipid-deficient mutant had significantly diminished Congo Red uptake though hexadecane-aqueous buffer partitioning was similar to H37Rv. An M. kansasii, ΔMKAN27435 partially lipooligosaccharide-deficient mutant absorbed marginally more Congo Red dye than the parent strain but was comparable in partition experiments. In evolving from ancestral mycobacteria, related to "M. canettii" and M. kansasii, modern M. tuberculosis probably became more hydrophobic by increasing the proportion of less polar lipids in the outer membrane. Importantly, such a change would enhance the capability for aerosol transmission, affecting virulence and pathogenicity