Involved in endoplasmic reticulum (ER) stress-mediated apoptosis through human Toll-like receptor 4 (TLR4) signaling pathway. Localizes to the host ER, leading to ER stress, disruption of intracellular Ca(2+) homeostasis and increase of nitric oxide (NO) and reactive oxygen species (ROS) levels. Stress response results in caspase-8 activation and apoptosis of macrophage cells. Apoptosis may lead to dissemination of the bacteria, thereby spreading the disease. Interacts with human TLR4. The PGRS region is important for localization and function. Belongs to the mycobacterial PE family. PGRS subfamily.