Journal Article

Deciphering the functional roles of PE18 and PPE26 proteins in modulating Mycobacterium tuberculosis pathogenesis and immune response

Hasnain, Seyed E., Shariq, Mohd, Ehtram, Aquib, Sheikh, Javaid Ahmad, Ehtesham, Nasreen Z., Pichipalli, Manjunath, Zarin, Sheeba, Quadir, Neha, Jamal, Salma

2025

Overview

Tuberculosis (TB), caused by (Mtb), remains a leading cause of mortality worldwide. A crucial factor in virulence is the ESX-5 secretion system, which transports PE/PPE proteins such as PE18 and PPE26. These proteins modulate host-pathogen interactions, immune responses, and intracellular survival mechanisms. Despite their importance, the roles and molecular interactions of PE18 and PPE26 in pathogenesis require further investigation. We explored the roles of PE18 and PPE26 using recombinant ( ) as a model organism. Protein-protein interactions were analyzed biochemically to identify partners within the ESX-5 secretion system, including EspG5 and other PE/PPE proteins. Subcellular localization of these proteins was assessed via cell fractionation studies. Functional assays, including cytokine production and antigen presentation studies, were performed using TLR2/Myd88 knockout and wild-type macrophages. experiments were conducted to assess effector T-cell activation and intracellular survival. Mechanistic insights into endosome-phagosome maturation and actin cytoskeleton dynamics were obtained through fluorescence microscopy. Our biochemical analyses confirmed interactions between PE18/PPE26, PE18/PPE27, PE19/PPE25, and EspG5/PPE, highlighting their involvement in ESX-5-mediated secretion. Cell fractionation studies revealed that PE/PPE proteins predominantly localize to the cell wall, with PE18 also secreted extracellularly. In vitro and experiments demonstrated that PE18 and PPE26 activate cytokine production and antigen presentation via TLR2/Myd88-dependent signaling pathways, inducing robust effector memory T-cell responses. Recombinant expressing PE18, PPE26, or their combination exhibited enhanced intracellular survival by disrupting endosome-phagosome maturation, likely through interference with actin cytoskeletal organization. Our findings elucidate the pivotal roles of PE18 and PPE26 in pathogenesis, emphasizing their contributions to immune modulation and intracellular persistence. The observed disruption of actin dynamics and endosome-phagosome maturation underscores a novel mechanism by which evades host defenses. The ability of PE18 and PPE26 to induce effector T-cell responses highlights their potential as targets for host-directed therapies or vaccine development against TB. Further studies focusing on their structure-function relationships and interactions with host proteins could accelerate the development of innovative therapeutic strategies.

• Publisher: Frontiers Media SA,Frontiers Media S.A
• Subject: Actin / Animals / Antigen presentation / Antigens, Bacterial - genetics / Antigens, Bacterial - immunology / Antigens, Bacterial - metabolism / Apoptosis / Autophagy / Bacterial Proteins - genetics / Bacterial Proteins - immunology / Bacterial Proteins - metabolism / Bone marrow / Cell activation / Cell survival / Cell walls / Cloning / Cytokines / Cytoskeleton / Endosomes / Fluorescence microscopy / Gene amplification / host-pathogen interaction / Host-pathogen interactions / Host-Pathogen Interactions - immunology / Humans / immune modulation / Immune response / Immunity (Disease) / Immunological memory / Immunology / Immunomodulation / Infections / Intracellular / Lymphocytes T / macrophage activation marker / Macrophages / Macrophages - immunology / Macrophages - metabolism / Macrophages - microbiology / Maturation / Medical innovations / Mice / Mice, Inbred C57BL / Mice, Knockout / Mycobacterium smegmatis - immunology / Mycobacterium tuberculosis / Mycobacterium tuberculosis - immunology / Mycobacterium tuberculosis - pathogenicity / MyD88 protein / Pathogenesis / Pathogens / phagosome / proinflammatory cytokine / Protein transport / Proteins / Roles / Th1 immune response / TLR2 protein / Toll-Like Receptor 2 - genetics / Tuberculosis / Tuberculosis - immunology / Tuberculosis - microbiology / Vaccine development / Virulence