Selection and application of peptide mimotopes of MPT64 protein in Mycobacterium tuberculosis

Molecular characterization of Mycobacterium tuberculosis through MPT64 gene polymorphism using next-generation sequencing technology

Aim: To characterize and analyze polymorphism of the MPT64 gene and evaluate AgMPT64-based immunochromatographic assay (ICA) specificity associated with polymorphism. Materials & methods: A total of 1449 suspected samples were tested for tuberculosis (TB), and the MPT64/rv1980c gene was sequenced using next-generation sequencing for polymorphism analysis. Results: Of the TB-positive individuals, 200 (13.80%), 186 (12.84%) and 129 (8.90%) were positive using the liquid culture, GeneXpert and fluorescence microscopy assays, respectively. Liquid culture medium-based samples were confirmed using ICA, in which 193 (96.5%) were positive while seven (3.5%) were negative. Out of 14 sequenced samples, seven were positive and seven negative; 13 were identical to the reference and just one (ICA positive) showed a C477A point mutation (F159L). Conclusion: The results indicate that AgMPT64 can be considered as a potent vaccine candidate.

Lysine acetylation of DosR regulates the hypoxia response of Mycobacterium tuberculosis

Tuberculosis caused by Mycobacterium tuberculosis (Mtb) infection remains a large global public health problem. One striking characteristic of Mtb is its ability to adapt to hypoxia and trigger the ensuing transition to a dormant state for persistent infection, but how the hypoxia response of Mtb is regulated remains largely unknown. Here we performed a quantitative acetylome analysis to compare the acetylation profile of Mtb under aeration and hypoxia, and showed that 377 acetylation sites in 269 Mtb proteins were significantly changed under hypoxia. In particular, deacetylation of dormancy survival regulator (DosR) at K182 promoted the hypoxia response in Mtb and enhanced the transcription of DosR-targeted genes. Mechanistically, recombinant DosR^K182R protein demonstrated enhanced DNA-binding activity in comparison with DosR^K182Q protein. Moreover, Rv0998 was identified as an acetyltransferase that mediates the acetylation of DosR at K182. Deletion of Rv0998 also promoted the adaptation of Mtb to hypoxia and the transcription of DosR-targeted genes. Mice infected with an Mtb strain containing acetylation-defective DosR^K182R had much lower bacterial counts and less severe histopathological impairments compared with those infected with the wild-type strain. Our findings suggest that hypoxia induces the deacetylation of DosR, which in turn increases its DNA-binding ability to promote the transcription of target genes, allowing Mtb to shift to dormancy under hypoxia.

Utility of dominant epitopes derived from cell-wall protein LppZ for immunodiagnostic of pulmonary tuberculosis

Background

Serological antibodies tests for tuberculosis (TB) are widely used in developing countries. They appear to have some advantages- faster, simple and could be used for extrapulmonary TB. However, most of current commercial TB serological tests are failed to provide sufficient sensitivity and specificity. Improved serological biomarkers were essential. In this study, we present an approach using peptide array to discover new immunodiagnostic biomarkers based on immunodominant epitopes of TB antigens.

Results

The Probable conserved lipoprotein LppZ, which is difficult to express and purify in vivo was selected as the model antigen. We use two-step screening for dominant epitope selection. Based on peptide array data from 170 TB patients and 41 control samples, two dominant epitopes were identified to have diagnostic value for TB patients. Truncation assay was used to identify the core reactive sequence. Peptide- based ELISA was used to evaluate the diagnostic ability of pep-LppZ-1 and pep-LppZ-13. Pep-LppZ-1 has a sensitivity of 49.2% and a specificity of 83.3% in TB diagnose. Pep-LppZ-13 has a sensitivity of 43.3% and a specificity of 88.5% in TB diagnose.

Conclusions

Our result demonstrated that peptide array screening would be an advantage strategy of screening TB diagnostic peptides.

Electronic supplementary material

The online version of this article (10.1186/s12865-018-0243-2) contains supplementary material, which is available to authorized users.

Electrochemical determination of M. tuberculosis antigen based on Poly(3,4-ethylenedioxythiophene) and functionalized carbon nanotubes hybrid platform

An electrochemical DNA aptasensor for the detection of Mycobacterium tuberculosis (M. tb) antigen MPT64, was developed using Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with carbon nanotubes (CNTs). The biotinylated aptamer was immobilized onto streptavidin attached to -COOH functionalized CNTs via streptavidin-biotin interaction. Various characterization studies as FT-IR, FE-SEM, EIS and DPV were done to validate each fabrication step of the aptasensor. Optimization studies related to aptamer concentration and response time were performed. The electrochemical signal generated from the aptamer-target molecule interaction was monitored electrochemically by differential pulse voltammetry in the presence of [Fe(CN)₆]^3-/4- as a redox probe. The aptasensor exhibited limit of detection of 0.5±0.2fgmL^-1 within 15min with stability of 27 days at 4°C and reusability of 7 times after repeated regeneration with 50mM NaOH. The potential application of the aptasensor was established by spike-in studies to obtain recovery in between (88-95)%.

Detection of Mycobacterium tuberculosis based on H37R(v) binding peptides using surface functionalized magnetic microspheres coupled with quantum dots – a nano detection method for Mycobacterium tuberculosis

Despite suffering from the major disadvantage of low sensitivity, microscopy of direct smear with the Ziehl–Neelsen stain is still broadly used for detection of acid-fast bacilli and diagnosis of tuberculosis. Here, we present a unique detection method of Mycobacterium tuberculosis (MTB) using surface functionalized magnetic microspheres (MMSs) coupled with quantum dots (QDs), conjugated with various antibodies and phage display-derived peptides. The principle is based upon the conformation of the sandwich complex composed of bacterial cells, MMSs, and QDs. The complex system is tagged with QDs for providing the fluorescent signal as part of the detection while magnetic separation is achieved by MMSs. The peptide ligand H8 derived from the phage display library Ph.D.-7 is developed for MTB cells. Using the combinations of MMS-polyclonal antibody+QD-H8 and MMS-H8+QD-H8, a strong signal of 10³ colony forming units (CFU)/mL H₃₇R_v was obtained with improved specificity. MS-H8+QD-H8 combination was further optimized by adjusting the concentrations of MMSs, QDs, and incubation time for the maximum detection signal. The limit of detection for MTB was found to reach 10³ CFU/mL even for the sputum matrices. Positive sputum samples could be distinguished from control. Thus, this novel method is shown to improve the detection limit and specificity of MTB from the sputum samples, and to reduce the testing time for accurate diagnosis of tuberculosis, which needs further confirmation of more clinical samples.

Dynamic evolution and immunoreactivity of aptamers binding to polyclonal antibodies against MPT64 antigen of Mycobacterium tuberculosis

Antibody responses can be useful markers of tuberculosis infection. However, the established immunoassay diagnostic method is limited by antigenic variability. Replacing the recombinant proteins with aptamers may overcome these antigenic challenges. In this study, we systematically monitored the selection process of aptamers against anti-MPT64 antibodies of Mycobacterium tuberculosis to obtain more aptamers for developing a multisite system to increase the sensitivity of TB serological diagnosis. Twelve high-affinity aptamers with distinctive secondary structures were obtained by analyzing the dynamic evolution of aptamers against anti-MPT64 antibodies in the process of system evolution of ligands by exponential enrichment (SELEX). Pocket and stem-loops were found to be the basis of these aptamers binding to antibodies. Point mutations of highly conserved nucleotides in the pocket and stem-loop structures resulted in decreased affinity of aptamers to targets. To test the potential of these aptamers for future use in a serological diagnostic tool, three high-affinity aptamers with different epitope specificities were applied as capture aptamer in an enzyme-linked immunosorbent assay (ELISA) with sera of TB patients. The results showed that three aptamers all effectively bound anti-MPT64 antibodies from TB patients and had high specificity and sensitivity. These aptamers with high immunoreactivity in human sera may represent an efficient and promising analogue of MPT64 and have potential to substitute MPT64 as a nucleic acid antigen in the serological diagnosis of TB. Moreover, these aptamers with different epitope specificities may facilitate the development of a sandwich assay platform or a multisite system to effectively capture more targets in sera.

Polymorphism of antigen MPT64 in Mycobacterium tuberculosis strains

We selected 180 clinical isolates of the Mycobacterium tuberculosis complex (MTBC) from patients in China and performed comparative sequence analysis of the mpt64 gene after amplification. From the results, we found that polymorphisms of the mpt64 gene in the MTBC may be the reason for changes in the antigen produced, which may in turn cause alterations of related functions, thereby allowing immune evasion.

A novel B-cell epitope identified within Mycobacterium tuberculosis CFP10/ESAT-6 protein

Background

The 10-kDa culture filtrate protein (CFP10) and 6-kDa early-secreted target antigen (ESAT-6) play important roles in mycobacterial virulence and pathogenesis through a 1∶1 complex formation (CFP10/ESAT-6 protein, CE protein), which have been used in discriminating TB patients from BCG-vaccinated individuals. The B-cell epitopes of CFP10 and ESAT-6 separately have been analyzed before, however, the epitopes of the CE protein are unclear and the precise epitope in the positions 40 to 62 of ESAT-6 is still unknown.

Methods

In the present study, we searched for the B-cell epitopes of CE protein by using phage-display library biopanning with the anti-CE polyclonal antibodies. The epitopes were identified by sequence alignment, binding affinity and specificity detection, generation of polyclonal mouse sera and detection of TB patient sera.

Results

One linear B-cell epitope (KWDAT) consistent with the 162^nd–166^th sequence of CE and the 57^th–61^st sequence of ESAT-6 protein was selected and identified. Significantly higher titers of E5 peptide-binding antibodies were found in the sera of TB patients compared with those of healthy individuals.

Conclusion

There was a B-cell epitope for CE and ESAT-6 protein in the position 40 to 62 of ESAT-6. E5 peptide may be useful in the serodiagnosis of tuberculosis, which need to be further confirmed by more sera samples.