The ESAT-6 Protein of Mycobacterium tuberculosis Interacts with Beta-2-Microglobulin (β2M) Affecting Antigen Presentation Function of Macrophage

• DOI: 10.1371/journal.ppat.1004446
• Publication Date: 2014-10-30T18:21:35Z
• Authors: Gopalkrishna Sreejit; Asma Ahmed; Nazia Parveen; Vishwanath Jha; Vijaya Lakshmi Va...; Sudip Ghosh; Sangita Mukhopadhyay
• Keywords: 0301 basic medicine; Antigen Presentation; Antigens, Bacterial; Virulence; QH301-705.5; Virulence Factors; Macrophages; Mycobacterium tuberculosis; RC581-607; Recombinant Proteins; Cell Line; 3. Good health; 03 medical and health sciences; Bacterial Proteins; Genes, Reporter; Two-Hybrid System Techniques; Animals; Humans; Tuberculosis; Immunologic diseases. Allergy; Biology (General); beta 2-Microglobulin; Research Article; Gene Library

ESAT-6, an abundantly secreted protein of Mycobacterium tuberculosis (M. tuberculosis) is an important virulence factor, inactivation of which leads to reduced virulence of M. tuberculosis. ESAT-6 alone, or in complex with its chaperone CFP-10 (ESAT-6:CFP-10), is known to modulate host immune responses; however, the detailed mechanisms are not well understood. The structure of ESAT-6 or ESAT-6:CFP-10 complex does not suggest presence of enzymatic or DNA-binding activities. Therefore, we hypothesized that the crucial role played by ESAT-6 in the virulence of mycobacteria could be due to its interaction with some host cellular factors. Using a yeast two-hybrid screening, we identified that ESAT-6 interacts with the host protein beta-2-microglobulin (β2M), which was further confirmed by other assays, like GST pull down, co-immunoprecipitation and surface plasmon resonance. The C-terminal six amino acid residues (90-95) of ESAT-6 were found to be essential for this interaction. ESAT-6, in complex with CFP-10, also interacts with β2M. We found that ESAT-6/ESAT-6:CFP-10 can enter into the endoplasmic reticulum where it sequesters β2M to inhibit cell surface expression of MHC-I-β2M complexes, resulting in downregulation of class I-mediated antigen presentation. Interestingly, the ESAT-6:β2M complex could be detected in pleural biopsies of individuals suffering from pleural tuberculosis. Our data highlight a novel mechanism by which M. tuberculosis may undermine the host adaptive immune responses to establish a successful infection. Identification of such novel interactions may help us in designing small molecule inhibitors as well as effective vaccine design against tuberculosis.