Disorder‐to‐order transition in PE–PPE proteins of Mycobacterium tuberculosis augments the pro‐pathogen immune response

Abstract

A growing body of evidence supports the hypothesis that intrinsically disordered proteins often mediate host–pathogen interactions and modulate host functions for pathogen survival and virulence. Mycobacterium tuberculosis (M.tb) has evolved largely through reductive evolution, with a few exceptions such as the glycine–alanine‐rich PE–PPE/PGRS protein family, which has been expanding in pathogenic mycobacteria. Here, our analyses of the M.tb proteome and secretome revealed that the PE–PGRS subfamily is enriched for disordered regions and disordered binding sites, pointing to their importance in host–pathogen interactions. As a case study, the secondary structure of PE35–PPE68 and PE32–PPE65 of the pathogenesis‐related RD1 and RD8 regions was analyzed through Fourier‐transform infrared spectroscopy. These disordered proteins displayed a considerable structural shift from disordered to ordered while engaged in the formation of complexes. While these proteins are immunogenic individually and enhance the pro‐pathogen response, their corresponding complexes enhanced the responses manifold as displayed here by PE35 and PPE68. It is likely that M.tb exploits such disorder–order structural dynamics as a strategy to mount a pro‐pathogen response and subvert host defense for productive infection. This functional gain also serves as a means to compensate genomic content loss due to reductive evolution.

Mycobacterium tuberculosis Protein PE6 (Rv0335c), a Novel TLR4 Agonist, Evokes an Inflammatory Response and Modulates the Cell Death Pathways in Macrophages to Enhance Intracellular Survival

“…pe6 cloned into pET-28a was used to express the recombinant protein in ClearColi ® BL21(DE3), an endotoxin-free strain (Lucigen, Middleton, WI, USA). The protein was purified as described earlier with minor modifications ( 28 ). Briefly, recombinant PE6 protein was expressed and purified from BL21 DE3 clear E. coli cells, induced with 0.5 mM Isopropyl ß-D-1-thiogalactopyranoside at 37°C for 4 h till OD 600 nm was reached between 0.4 and 0.6.…”

“…We have earlier reported that co-operonic PE32–PPE65 hamper the production of Th1 response ( 27 ). Biophysical investigations revealed that this co-operonic interaction involves disorder-to-order transition that impacts inflammatory cytokines production ( 28 ).…”

Mycobacterium tuberculosis Specific Protein Rv1509 Evokes Efficient Innate and Adaptive Immune Response Indicative of Protective Th1 Immune Signature

“…Also, the intrinsically disordered regions of Rv1509 may play a pivotal role in performing important roles in protein function. It has been previously shown that intrinsically disordered regions in proteins may undergo a conformational change to facilitate different functions of a protein, including immune modulation ( 51 ). Besides, the cysteine residues present in Rv1509 can also contribute to modulating protein functions by changing their redox state, which involves changes in intracellular/intercellular disulphide bond ( 52 ).…”

Immunodominant Mycobacterium tuberculosis Protein Rv1507A Elicits Th1 Response and Modulates Host Macrophage Effector Functions

“…These disordered regions provide structural plasticity and conformational adaptability to proteins to enhance their binding promiscuity with various ligands. This could help pathogens to compensate for the genome reduction due to reductive evolution ( 59 ) by resorting to disordered proteins, moonlighting functions and protein promiscuity ( 45 , 60 , 61 ). In-silico analysis for epitope prediction and antigenicity revealed that this protein is highly antigenic.…”