Draper P
National Institute for Medical Research, Mill Hill, London NW7 1AA, England.
Front Biosci. 1998 Dec 15;3:D1253-61. doi: 10.2741/a360.
The permeability of mycobacteria to substances in their environment is controlled by the properties of their envelopes. Two special features are important: an outer lipid barrier based on a monolayer of characteristic mycolic acids and a capsule-like coat of polysaccharide and protein. The mycolate layer prevents entry of small hydrophilic molecules, which obtain access to the cell by way of pore-forming proteins resembling porins of Gram-negative bacteria. More lipophilic molecules can diffuse through the lipid layer. The capsule probably impedes access by macromolecules; in intracellular pathogenic species it forms the electron-transparent zone that separates the bacterium from the membrane of the host phagosome. The structure of the outer lipid barrier seems common to all mycobacteria, fast- and slow-growing, but the capsule is more abundant in slow-growing species, a group which includes all the important mycobacterial pathogens. Mycobacteria secrete proteins into their environment, which are likely to be important in the pathogenesis of mycobacterial diseases. Knowledge of how these proteins, and the polysaccharides of the capsule, cross the outer lipid barrier is minimal at present. It is likely that proper knowledge of mycobacterial permeability will enable new approaches to treatment of mycobacterial disease.
分枝杆菌对其周围环境中物质的通透性由其包膜特性控制。有两个特殊特征很重要：一个基于单层特征性分枝菌酸的外部脂质屏障，以及一层多糖和蛋白质组成的类似荚膜的外层。分枝菌酸层可阻止小的亲水分子进入，这些亲水分子通过类似于革兰氏阴性菌孔蛋白的成孔蛋白进入细胞。亲脂性更强的分子可以扩散穿过脂质层。荚膜可能会阻碍大分子进入；在细胞内致病菌种中，它形成电子透明区，将细菌与宿主吞噬体膜分隔开。外部脂质屏障的结构似乎在所有分枝杆菌中都很常见，包括快速生长和缓慢生长的，但荚膜在缓慢生长的菌种中更为丰富，这一类包括所有重要的分枝杆菌病原体。分枝杆菌向其周围环境分泌蛋白质，这些蛋白质可能在分枝杆菌疾病的发病机制中起重要作用。目前，对于这些蛋白质以及荚膜多糖如何穿过外部脂质屏障的了解还很少。对分枝杆菌通透性的恰当了解可能会带来治疗分枝杆菌疾病的新方法。
