Fractionation and analysis of mycobacterial proteins

Mycobacterial resistance to zinc poisoning requires assembly of P-ATPase-containing membrane metal efflux platforms

The human pathogen Mycobacterium tuberculosis requires a P_1B-ATPase metal exporter, CtpC (Rv3270), for resistance to zinc poisoning. Here, we show that zinc resistance also depends on a chaperone-like protein, PacL1 (Rv3269). PacL1 contains a transmembrane domain, a cytoplasmic region with glutamine/alanine repeats and a C-terminal metal-binding motif (MBM). PacL1 binds Zn²⁺, but the MBM is required only at high zinc concentrations. PacL1 co-localizes with CtpC in dynamic foci in the mycobacterial plasma membrane, and the two proteins form high molecular weight complexes. Foci formation does not require flotillin nor the PacL1 MBM. However, deletion of the PacL1 Glu/Ala repeats leads to loss of CtpC and sensitivity to zinc. Genes pacL1 and ctpC appear to be in the same operon, and homologous gene pairs are found in the genomes of other bacteria. Furthermore, PacL1 colocalizes and functions redundantly with other PacL orthologs in M. tuberculosis. Overall, our results indicate that PacL proteins may act as scaffolds that assemble P-ATPase-containing metal efflux platforms mediating bacterial resistance to metal poisoning.

The human pathogen Mycobacterium tuberculosis requires a metal exporter, CtpC, for resistance to zinc poisoning. Here, the authors show that zinc resistance also depends on a chaperone-like protein that binds zinc ions, forms high-molecular-weight complexes with CtpC in the cytoplasmic membrane, and is required for CtpC function.

Protein profile of different cellular fractions from Mycobacterium tuberculosis strains after exposure to isoniazid

Different biochemical studies looking for the effect of INH on the physiology of Mycobacterium tuberculosis (Mtb) have been conducted. Here, we present a detailed analysis, looking at the protein variation in the Mtb cell due to exposure of sub-inhibitory concentrations of INH, evaluating three different variables: cellular fraction, genetic lineage, and INH phenotypic profile. Mass spectrometry analysis demonstrated that the most significantly affected cellular fraction was the membrane and the INH resistant strains showed the highest number of proteins altered when they were exposed to INH. Raw data are available via ProteomeXchange with identifier PXD007588.

Biochemical Characterization of Isoniazid-resistant Mycobacterium tuberculosis: Can the Analysis of Clonal Strains Reveal Novel Targetable Pathways?

Tuberculosis (TB) continues to be an important public health threat worldwide, due in part to drug resistant Mycobacterium tuberculosis (Mtb) strains. The United States recently reported a shortage of isoniazid (INH), which could drive higher INH resistance rates. Changes in the Mtb proteome before and after acquisition of INH resistance in a clean genetic background remain understudied and may elucidate alternate drug targets. Here, we focused on Mtb clonal strains to characterize the consequences of INH resistance on mycobacterial metabolism. Proteomic analysis was conducted by liquid-chromatography tandem mass spectrometry (LC-MS/MS) of cellular and secreted fractions, followed by a normalized spectral counting (NSAF) analysis (data are available via ProteomeXchange with identifier PXD009549). Two different Mtb clonal pairs representing a specific genetic lineage (one clinical and one generated in the laboratory) but sharing a katG mutation associated with INH resistance, were used in our analysis. Overall, we found 26 Mtb proteins with altered abundances after acquisition of INH resistance across both Mtb genetic lineages studied. These proteins were involved in ATP synthesis, lipid metabolism, regulatory events, and virulence, detoxification, and adaptation processes. Proteomic findings were validated by Western blotting analyses whenever possible. Mycolic acid (MA) analysis through LC/MS in the clonal Mtb pairs did not reveal a common trend in the alteration of these fatty acids across both INHr strains but revealed a significant reduction in levels of the two more abundant α-MA features in the clinical INHr strain. Interestingly, the clinical clonal pair demonstrated more variation in the abundance of the proteins involved in the FAS II pathway. Together, the proteomic and lipidomic data highlight the identification of potential drug targets such as alternative lipid biosynthetic pathways that may be exploited to combat clinically relevant Mtb INHr strains.

Interplay of strain and race/ethnicity in the innate immune response to M. tuberculosis

Background

The roles of host and pathogen factors in determining innate immune responses to M. tuberculosis are not fully understood. In this study, we examined host macrophage immune responses of 3 race/ethnic groups to 3 genetically and geographically diverse M. tuberculosis lineages.

Methods

Monocyte-derived macrophages from healthy Filipinos, Chinese and non-Hispanic White study participants (approximately 45 individuals/group) were challenged with M. tuberculosis whole cell lysates of clinical strains Beijing HN878 (lineage 2), Manila T31 (lineage 1), CDC1551 (lineage 4), the reference strain H37Rv (lineage 4), as well as with Toll-like receptor 2 agonist lipoteichoic acid (TLR2/LTA) and TLR4 agonist lipopolysaccharide (TLR4/LPS). Following overnight incubation, multiplex assays for nine cytokines: IL-1β, IL-2, IL-6, IL-8, IL-10, IL-12p70, IFNγ, TNFα, and GM-CSF, were batch applied to supernatants.

Results

Filipino macrophages produced less IL-1, IL-6, and more IL-8, compared to macrophages from Chinese and Whites. Race/ethnicity had only subtle effects or no impact on the levels of IL-10, IL-12p70, TNFα and GM-CSF. In response to the Toll-like receptor 2 agonist lipoteichoic acid (TLR2/LTA), Filipino macrophages again had lower IL-1 and IL-6 responses and a higher IL-8 response, compared to Chinese and Whites. The TLR2/LTA-stimulated Filipino macrophages also produced lower amounts of IL-10, TNFα and GM-CSF. Race/ethnicity had no impact on IL-12p70 levels released in response to TLR2/LTA. The responses to TLR4 agonist lipopolysaccharide (TLR4/LPS) were similar to the TLR2/LTA responses, for IL-1, IL-6, IL-8, and IL-10. However, TLR4/LPS triggered the release of less IL-12p70 from Filipino macrophages, and less TNFα from White macrophages.

Conclusions

Both host race/ethnicity and pathogen strain influence the innate immune response. Such variation may have implications for the development of new tools across TB therapeutics, immunodiagnostics and vaccines.

Potential of High-Affinity, Slow Off-Rate Modified Aptamer Reagents for Mycobacterium tuberculosis Proteins as Tools for Infection Models and Diagnostic Applications

Direct pathogen detection in blood to diagnose active tuberculosis (TB) has been difficult due to low levels of circulating antigens or due to the lack of specific, high-affinity binding reagents and reliable assays with adequate sensitivity. We sought to determine whether slow off-rate modified aptamer (SOMAmer) reagents with subnanomolar affinity for Mycobacterium tuberculosis proteins (antigens 85A, 85B, 85C, GroES, GroEL2, DnaK, CFP10, KAD, CFP2, RplL, and Tpx) could be useful to diagnose tuberculosis. When incorporated into the multiplexed, array-based proteomic SOMAscan assay, limits of detection reached the subpicomolar range in 40% serum. Binding to native M. tuberculosis proteins was confirmed by using M. tuberculosis culture filtrate proteins and fractions from infected macrophages and via affinity capture assays and subsequent mass spectrometry. Comparison of serum from culture-positive pulmonary TB patients and TB suspects systematically ruled out for TB revealed small but statistically significant (P < 0.0001) differences in the median M. tuberculosis signals and in specific pathogen markers, such as antigen 85B. Samples where many M. tuberculosis aptamers produced high signals were rare exceptions. In concentrated, protein-normalized urine from TB patients and non-TB controls, the CFP10 (EsxB) SOMAmer yielded the most significant differential signals (P < 0.0276), particularly in TB patients with HIV coinfection. In conclusion, direct M. tuberculosis antigen detection proved difficult even with a sensitive method such as SOMAscan, likely due to their very low, subpicomolar abundance. The observed differences between cases and controls had limited diagnostic utility in serum and urine, but further evaluation of M. tuberculosis SOMAmers using other platforms and sample types is warranted.