Inactivation of the antigen 85C gene profoundly affects the mycolate content and alters the permeability of the Mycobacterium tuberculosis cell envelope
M. Jackson et al., Inactivation of the antigen 85C gene profoundly affects the mycolate content and alters the permeability of the Mycobacterium tuberculosis cell envelope, MOL MICROB, 31(5), 1999, pp. 1573-1587
The antigen 85 complex of Mycobacterium tuberculosis consists of three abun
dantly secreted proteins. The recent characterization of a mycoloyltransfer
ase activity associated in vitro with each of these antigens suggested that
they are potentially important for the building of the unusual cell envelo
pe of mycobacteria. To define the physiological role of these proteins, the
gene coding for antigen 85C was inactivated by transposon mutagenesis. The
resulting mutant was shown to transfer 40% fewer mycolates to the cell wal
l with no change in the types of mycolates esterifying arabinogalactan or i
n the composition of non-covalently linked mycolates. As a consequence, the
diffusion of the hydrophobic chenodeoxycholate and the hydrophilic glycero
l, but not that of isoniazid, was found to be much faster through the cell
envelope of the mutant than that of the parent strain. Taken together, thes
e data demonstrate that: (i) antigen 85C is involved directly or indirectly
in the transfer of mycolates onto the cell wall of the whole bacterium; (i
i) the enzyme is not specific for a given type of mycolate; and (iii) the c
ell wall-linked mycolate layer may represent a barrier for the diffusion of
small hydrophobic and hydrophilic molecules.