Department of Infectious Diseases and Microbiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
J Biol Chem. 2010 Jun 4;285(23):17380-9. doi: 10.1074/jbc.M110.112813. Epub 2010 Apr 7.
Mycobacterial species, like other microbes, spontaneously form multicellular drug-tolerant biofilms when grown in vitro in detergent-free liquid media. The structure of Mycobacterium tuberculosis biofilms is formed through genetically programmed pathways and is built upon a large abundance of novel extracellular free mycolic acids (FM), although the mechanism of FM synthesis remained unclear. Here we show that the FM in Mycobacterium smegmatis biofilms is produced through the enzymatic release from constitutively present mycolyl derivatives. One of the precursors for FM is newly synthesized trehalose dimycolate (TDM), which is cleaved by a novel TDM-specific serine esterase, Msmeg_1529. Disruption of Msmeg_1529 leads to undetectable hydrolytic activity, reduced levels of FM in the mutant, and retarded biofilm growth. Furthermore, enzymatic hydrolysis of TDM remains conserved in M. tuberculosis, suggesting the presence of a TDM-specific esterase in this pathogen. Overall, this study provides the first evidence for an enzymatic release of free mycolic acids from cell envelope mycolates during mycobacterial growth.
分枝杆菌属的微生物与其他微生物一样，在无清洁剂的液体培养基中体外生长时，会自发形成多细胞药物耐受生物膜。结核分枝杆菌生物膜的结构是通过基因编程途径形成的，其基础是大量新型的游离分枝菌酸（FM），尽管 FM 合成的机制尚不清楚。在这里，我们表明分枝杆菌属的生物膜中的 FM 是通过酶从组成型存在的类脂酰衍生物中释放出来的。FM 的前体之一是新合成的海藻糖二分枝菌酸（TDM），它被一种新型的 TDM 特异性丝氨酸酯酶 Msmeg_1529 切割。Msmeg_1529 的缺失会导致水解活性不可检测、突变体中 FM 水平降低以及生物膜生长受阻。此外，TDM 的酶促水解在结核分枝杆菌中仍然保守，这表明该病原体中存在 TDM 特异性酯酶。总的来说，这项研究首次提供了分枝杆菌生长过程中从细胞包膜类脂酰释放游离分枝菌酸的酶促释放的证据。
