Abstract:
Mycolic acids constitute the waxy layer of the outer cell wall of Mycobacterium spp and
a few other genera. They are diverse in structure, providing a unique chromatographic foot-print
for almost each of the more than seventy Mycobacterium species. Although mainly esterified to
cell wall arabinogalactan, trehalose or glucose, some free mycolic acid is secreted during in vitro
growth of M. tuberculosis. In M. tuberculosis, alpha-, keto- and methoxy-mycolic acids are the
main classes, each differing in their ability to attract neutrophils, induce foamy macrophages or
adopt an antigenic structure for antibody recognition. Of interest is their particular relationship to
cholesterol, discovered by their ability to attract cholesterol, to bind Amphotericin B or to be
recognised by monoclonal antibodies that cross-react with cholesterol. The structural elements
that determine this diverse functionality include the carboxylic acid in the mycolic motif, as well
as the nature and stereochemistry of the two functional groups in the merochain. The functional
diversity of mycolic acid classes implies that much information may be contained in the selective
expression and secretion of mycolic acids to establish tuberculosis after infection of the host.
Their cholesteroid nature may relate to how they utilize host cholesterol for their persistent
survival.
