结核分枝杆菌(Mtb)是在巨噬细胞中存活和生长的细胞内病原体。Mtb用于实现细胞内存活的机制是分泌阻止吞噬体成熟正常过程的效应分子。通过吞噬体成熟停滞(PMA),Mtb保留在早期吞噬体中并避免递送至降解吞噬溶酶体。Mtb的一种PMA效应是分泌的SapM磷酸酶。因为SapM的主机目标,磷脂酰肌醇-3-磷酸酯(PI3P),位于吞噬体的细胞溶质表面,SapM不仅需要由分枝杆菌释放,而且还需要离开吞噬体才能发挥其功能。迄今为止,已知Mtb分子离开吞噬体的唯一机制是ESX-1分泌系统的吞噬体透化。要了解PMA中SapM函数的这一步,我们在两种减毒牛分枝杆菌卡介苗(BCG)疫苗株中产生了相同的框内sapM突变体,缺少ESX-1系统,Mtb。这些突变体的表征表明SapM是BCG和Mtb中PMA所必需的。Further,通过在BCG中建立SAPM在PMA中的作用,随后在缺乏ESX-1系统的Mtb突变体中,我们证明了SapM的作用不需要ESX-1。我们进一步确定ESX-2或ESX-4也不是SapM在PMA中发挥作用所必需的。这些结果表明,SapM是BCG和Mtb中PMA的分泌效应物,并且它可以独立于Mtb分子离开吞噬体的已知机制而起作用。
Mycobacterium tuberculosis (Mtb) is an intracellular pathogen that survives and grows in macrophages. A mechanism used by Mtb to achieve intracellular survival is to secrete effector molecules that arrest the normal process of phagosome maturation. Through phagosome maturation arrest (PMA), Mtb remains in an early phagosome and avoids delivery to degradative phagolysosomes. One PMA effector of Mtb is the secreted SapM phosphatase. Because the host target of SapM, phosphatidylinositol-3-phosphate (PI3P), is located on the cytosolic face of the phagosome, SapM needs to not only be released by the mycobacteria but also travel out of the phagosome to carry out its function. To date, the only mechanism known for Mtb molecules to leave the phagosome is phagosome permeabilization by the ESX-1 secretion system. To understand this step of SapM function in PMA, we generated identical in-frame sapM mutants in both the attenuated Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccine strain, which lacks the ESX-1 system, and Mtb. Characterization of these mutants demonstrated that SapM is required for PMA in BCG and Mtb. Further, by establishing a role for SapM in PMA in BCG, and subsequently in a Mtb mutant lacking the ESX-1 system, we demonstrated that the role of SapM does not require ESX-1. We further determined that ESX-2 or ESX-4 is also not required for SapM to function in PMA. These results indicate that SapM is a secreted effector of PMA in both BCG and Mtb, and that it can function independent of the known mechanism for Mtb molecules to leave the phagosome.