Serine protease Rv2569c facilitates transmission of Mycobacterium tuberculosis via disrupting the epithelial barrier by cleaving E-cadherin.

Epithelial cells function as the primary line of defense against invading pathogens. However, bacterial pathogens possess the ability to compromise this barrier and facilitate the transmigration of bacteria. Nonetheless, the specific molecular mechanism employed by Mycobacterium tuberculosis (M.tb) in this process is not fully understood. Here, we investigated the role of Rv2569c in M.tb translocation by assessing its ability to cleave E-cadherin, a crucial component of cell-cell adhesion junctions that are disrupted during bacterial invasion. By utilizing recombinant Rv2569c expressed in Escherichia coli and subsequently purified through affinity chromatography, we demonstrated that Rv2569c exhibited cell wall-associated serine protease activity. Furthermore, Rv2569c was capable of degrading a range of protein substrates, including casein, fibrinogen, fibronectin, and E-cadherin. We also determined that the optimal conditions for the protease activity of Rv2569c occurred at a temperature of 37°C and a pH of 9.0, in the presence of MgCl2. To investigate the function of Rv2569c in M.tb, a deletion mutant of Rv2569c and its complemented strains were generated and used to infect A549 cells and mice. The results of the A549-cell infection experiments revealed that Rv2569c had the ability to cleave E-cadherin and facilitate the transmigration of M.tb through polarized A549 epithelial cell layers. Furthermore, in vivo infection assays demonstrated that Rv2569c could disrupt E-cadherin, enhance the colonization of M.tb, and induce pathological damage in the lungs of C57BL/6 mice. Collectively, these results strongly suggest that M.tb employs the serine protease Rv2569c to disrupt epithelial defenses and facilitate its systemic dissemination by crossing the epithelial barrier.

Mycobacterium tuberculosis protease Rv3090 is associated with late cell apoptosis and participates in organ injuries and mycobacterial dissemination in mice.

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (Mtb). Mtb can overcome macrophage intracellular killing and lead to persistent infections. The proteases of Mtb are critical virulence factors that participate in immune responses. We determined that Rv3090 is a cell wall-associated protease and a potential pathogenic factor. To characterize the role of Rv3090 in Mtb, recombinant Msg_Rv3090 and Msg_pAIN strains were constructed to infect macrophages and mice. Lactate dehydrogenase assays and flow cytometry results showed that Rv3090 induces late macrophage apoptosis. In vivo infection experiments indicated that Rv3090 could induce hepatocyte and lung cell apoptosis and cause pathological damage to the spleen, livers and lungs. Msg_Rv3090 specifically stimulated the secretion of inflammatory cytokines including TNF-α, IL-6 and IL-1ß. Overexpression of Rv3090 significantly promoted the survival of Msg in livers and lungs. Thus, Rv3090 protease triggered late cell apoptosis and contributed to the pathogenicity and dissemination of Mtb.

A unique combination of glycoside hydrolases in Streptococcus suis specifically and sequentially acts on host-derived αGal-epitope glycans.

Infections by many bacterial pathogens rely on their ability to degrade host glycans by producing glycoside hydrolases (GHs). Here, we discovered a conserved multifunctional GH, SsGalNagA, containing a unique combination of two family 32 carbohydrate-binding modules (CBM), a GH16 domain and a GH20 domain, in the zoonotic pathogen Streptococcus suis 05ZYH33. Enzymatic assays revealed that the SsCBM-GH16 domain displays endo-(ß1,4)-galactosidase activity specifically toward the host-derived αGal epitope Gal(α1,3)Gal(ß1,4)Glc(NAc)-R, whereas the SsGH20 domain has a wide spectrum of exo-ß-N-acetylhexosaminidase activities, including exo-(ß1,3)-N-acetylglucosaminidase activity, and employs this activity to act in tandem with SsCBM-GH16 on the αGal-epitope glycan. Further, we found that the CBM32 domain adjacent to the SsGH16 domain is indispensable for SsGH16 catalytic activity. Surface plasmon resonance experiments uncovered that both CBM32 domains specifically bind to αGal-epitope glycan, and together they had a KD of 3.5 mm toward a pentasaccharide αGal-epitope glycan. Cell-binding and αGal epitope removal assays revealed that SsGalNagA efficiently binds to both swine erythrocytes and tracheal epithelial cells and removes the αGal epitope from these cells, suggesting that SsGalNagA functions in nutrient acquisition or alters host signaling in S. suis Both binding and removal activities were blocked by an αGal-epitope glycan. SsGalNagA is the first enzyme reported to sequentially act on a glycan containing the αGal epitope. These findings shed detailed light on the evolution of GHs and an important host-pathogen interaction.

Characterization and pathogenicity of extracellular serine protease MAP3292c from Mycobacterium avium subsp. paratuberculosis.

Serine protease is the virulence factor of many pathogens. However, there are no prevailing data available for serine protease as a virulence factor derived from Mycobacterium avium subsp. paratuberculosis (MAP). The MAP3292c gene from MAP, the predicted serine protease, was expressed in Escherichia coli and characterized by biochemical methods. MAP3292c protein efficiently hydrolyzed casein at optimal temperature and pH of 41 °C and 9.0, respectively. Furthermore, divalent metal ions of Ca2+ significantly promoted the protease activity of MAP3292c, and MAP3292c had autocleavage activity between serine 86 and asparagine 87. Site-directed mutagenesis studies showed that the serine 238 residue had catalytic roles in MAP3292c. Furthermore, a BALB/c mouse model confirmed that MAP3292c significantly promoted the survival of Mycobacterium smegmatis in vivo; caused damage to the liver, spleen, and lung; and promoted the release of inflammatory cytokines IL-1ß, IL-6, and TNF-α in mice. Finally, we confirmed that MAP3292c was relevant to mycobacterial pathogenicity.

The prominent alteration in transcriptome and metabolome of Mycobacterium bovis BCG str. Tokyo 172 induced by vitamin B1.

BACKGROUND: Vitamin B1 (VB1) is a crucial dietary nutrient and essential cofactor for several key enzymes in the regulation of cellular and metabolic processes, and more importantly in the activation of immune system. To date, the precise role of VB1 in Mycobacterium tuberculosis remains to be fully understood. RESULTS: In this study, the transcriptional and metabolic profiles of VB1-treated Mycobacterium. bovis BCG were analyzed by RNA-sequencing and LC-MS (Liquid chromatography coupled to mass spectrometry). The selection of BCG strain was based on its common physiological features shared with M. tuberculosis. The results of cell growth assays demonstrated that VB1 inhibited the BCG growth rate in vitro. Transcriptomic analysis revealed that the expression levels of genes related to fatty acid metabolism, cholesterol metabolism, glycolipid catabolism, DNA replication, protein translation, cell division and cell wall formation were significantly downregulated in M. bovis BCG treated with VB1. In addition, the metabolomics LC-MS data indicated that most of the amino acids and adenosine diphosphate (ADP) were decreased in M. bovis BCG strain after VB1 treatment. CONCLUSIONS: This study provides the molecular and metabolic bases to understand the impacts of VB1 on M.bovis BCG.

PE17 protein from Mycobacterium tuberculosis enhances Mycobacterium smegmatis survival in macrophages and pathogenicity in mice.

The capacity of Mycobacterium tuberculosis to survive and cause disease is strongly correlated with its ability to escape multiple defense strategies in hosts. In particular, M. tuberculosis has the remarkable capacity to survive within the hostile environment of macrophages. Here, we found that the PE17 (Rv1646) protein promoted intracellular survival of M. smegmatis in peritoneal macrophages from mice. Further experiments confirmed that the recombinant PE17 protein was localized in the cell wall of M. smegmatis. Results from the macrophage infection model showed that PE17 significantly downregulated pro-inflammatory cytokines (interleukin-6, interleukin-12, and tumer necrosis factor-α) secretion from macrophages induced by M. smegmatis and promoted macrophage necrosis. Furthermore, a C57BL/6 mouse infection model confirmed that PE17 significantly prolonged the survival of M. smegmatis in vivo and aggravated lesions in organs of infected mice. Moreover, persistent high levels of interferon-γ and interleukin-1ß in infected mice indicated that the bacteria were not easily removed in vivo. Overall, our present results suggested that the PE17 may act as an important pathogenic factor in M. tuberculosis.

Characterization of a novel exported esterase Rv3036c from Mycobacterium tuberculosis.

Mycobacterium tuberculosis possesses an unusually high number of genes involved in the metabolism of lipids. Driven by a newly described esterase motif SXXK in the amino acid sequence and a predicted signal peptide, the gene rv3036c from M. tuberculosis was cloned and characterized biochemically. Rv3036c efficiently hydrolyzes soluble p-nitrophenyl esters but not emulsified lipid. The highest activity of this enzyme was observed when p-nitrophenyl acetate (C2) was used as the substrate. Based on the activities, Rv3036c was classified as a nonlipolytic hydrolase. The results of immunoreactivity studies on the subcellular mycobacterial fractions suggested that the enzyme was present in the cell wall and cell membrane in mycobacteria. In summary, Rv3036c was characterized as a novel cell wall-anchored esterase from M. tuberculosis.

PE12 interaction with TLR4 promotes intracellular survival of Mycobacterium tuberculosis by suppressing inflammatory response.

Macrophages serve as the primary immune cells responsible for the innate immune defense against Mycobacterium tuberculosis (MTB) infection within the host. Specifically, NLRP3, a member of the NLRs family, plays a significant role in conferring resistance against MTB infection. Conversely, MTB evades innate immune killing by impeding the activation of the NLRP3 inflammasome, although the precise mechanism remains uncertain. In this study, we have identified PE12 (Rv1172c), a member of the PE/PPE family proteins, as an extracellular protein of MTB. PE12 interacts with Toll like receptor 4 (TLR4) in macrophages, forming the PE12-TLR4 complex which subsequently inhibits the transcription and expression of NLRP3. As a result, the transcription and secretion of IL-1ß are reduced through the PE12-TLR4-NLRP3-IL-1ß immune pathway. In vitro and in vivo experiments using a PE12-deficient strain (H37RvΔPE12) demonstrate a weakening of the suppression of the inflammatory response to MTB infection. Our findings highlight the role of the PE12 protein in not only inhibiting the transcription and release of inflammatory cytokines but also mediating the killing of MTB escape macrophages through TLR4 and inducing lung injury in MTB-infected mice. These results provide evidence that PE12 plays a significant role in the inhibition of the host immune response by MTB.

DosR's multifaceted role on Mycobacterium bovis BCG revealed through multi-omics.

Mycobacterium tuberculosis (Mtb) is an intracellular bacterium that causes a highly contagious and potentially lethal tuberculosis (TB) in humans. It can maintain a dormant TB infection within the host. DosR (dormancy survival regulator) (Rv3133c) has been recognized as one of the key transcriptional proteins regulating bacterial dormancy and participating in various metabolic processes. In this study, we extensively investigate the still not well-comprehended role and mechanism of DosR in Mycobacterium bovis (M. bovis) Bacillus Calmette-Guérin (BCG) through a combined omics analysis. Our study finds that deleting DosR significantly affects the transcriptional levels of 104 genes and 179 proteins. Targeted metabolomics data for amino acids indicate that DosR knockout significantly upregulates L-Aspartic acid and serine synthesis, while downregulating seven other amino acids, including L-histidine and lysine. This suggests that DosR regulates amino acid synthesis and metabolism. Taken together, these findings provide molecular and metabolic bases for DosR effects, suggesting that DosR may be a novel regulatory target.

A candidate subunit vaccine induces protective immunity against Mycobacterium avium subspecies paratuberculosis in mice.

Mycobacterium avium subspecies paratuberculosis (MAP) causes paratuberculosis (PTB), which is a granulomatous enteritis in ruminants that threatens the dairy industry's healthy development and public health safety worldwide. Because the commercial inactivated vaccines are not completely protective and interfere with bovine tuberculosis diagnostics, we tested four fusion proteins, namely 66NC, 66CN, 90NC, and 90CN, which were constructed with MAP3527, Ag85B, and Hsp70 of MAP in different tandem combinations. Notably, 66NC, which encodes a 66 kDa fusion protein that combines in linear order MAP3527N40-232, Ag85B41-330, and MAP3527C231-361, induced a powerful and specific IFN-γ response. Immunization of C57BL/6 mice with the 66NC fusion protein formulated in Montanide ISA 61 VG adjuvant generated robust Th1, Th2, and Th17 type immune responses and strong antibody responses. The 66NC vaccine protected C57BL/6 mice against virulent MAP K-10 infection. This resulted in a reduction of bacterial load and improvement of pathological damage in the liver and intestine, in addition to a reduction of body weight loss; significantly better protection than the reported 74 F vaccine was also induced. Furthermore, vaccine efficacy correlated with the levels of IFN-γ-, TNF-α-, and IL-17A-secreting antigen-specific CD4+ and CD8+ T lymphocytes as well as with serum IFN-γ and TNF-α levels after vaccination. These results demonstrate that recombinant protein 66NC is an efficient candidate for further development into a protective vaccine in terms of inducing specific protection against MAP.

Extracellular DNase MAP3916c attacks the neutrophil extracellular traps and is needed for Mycobacterium avium subsp. paratuberculosis virulence.

Extracellular DNases/nucleases are important virulence factors in many bacteria. However, no DNase/nucleases have been reported in Mycobacterium avium subsp. paratuberculosis (MAP), which is a pathogen of paratuberculosis. Genome analyses of MAP K-10 revealed that the map3916c gene putatively encodes a nuclease. In this study, we show that MAP3916c is an extracellular nonspecific DNase requiring a divalent cation, especially Mg2+. The optimum DNase activity of MAP3916c was exhibited at 41 °C and pH 9.0. Site-directed mutagenesis studies indicated that 125-Histidine is necessary for MAP3916c DNase activity. In addition, MAP3916c DNase could destroy the neutrophil extracellular traps (NETs) induced by Phorbol 12-myristate 13-acetate in vitro and degrade the NETs induced by MAP K-10 upon infection. Furthermore, MAP3916c DNase promoted the colonization of MAP K-10, induced the formation of granulomas in the liver and small intestine and promoted the release of IL-1ß, IL-6 and TNF-α inflammatory cytokines during the infection of mice. These results indicated that MAP3916c is relevant to NETs escape and the pathogenicity of MAP. It also provides a basis for further study of the function of nuclease activity on the MAP immune evasion.

DosR Regulates the Transcription of the Arginine Biosynthesis Gene Cluster by Binding to the Regulatory Sequences in Mycobacterium bovis Bacille Calmette-Guerin.

l-Arginine serves as a carbon and nitrogen source and is critical for Mycobacterium tuberculosis (Mtb) survival in the host. Generally, ArgR acts as a repressor regulating arginine biosynthesis by binding to the promoter of the argCJBDFGH gene cluster. In this study, we report that the dormancy regulator DosR is a novel arginine regulator binding to the promoter region of argC (rv1652), which regulates arginine synthesis. Phosphorylation modification promoted DosR binding to a region upstream of the promoter. Cofactors, including arginine and metal ions, had an inhibitory effect on this association. Furthermore, DosR regulatory function relies on the interaction of the 167, 181, 182, and 197 amino acid residues with an inverse complementary sequence. Arginine also binds to DosR and directly affects its DNA-binding ability. Together, the results demonstrate that DosR acts as a novel transcriptional regulator of arginine synthesis in Mycobacterium bovis bacille Calmette-Guerin.

Serological investigation and genotyping of Mycobacterium avium subsp. paratuberculosis in sheep and goats in Inner Mongolia, China.

Paratuberculosis a contagious and chronic disease in domestic and wild ruminants, is caused by Mycobacterium avium subspecies paratuberculosis (MAP). Typical clinical signs include intractable diarrhea, progressive emaciation, proliferative enteropathy, and mesenteric lymphadenitis. Paratuberculosis is endemic to many parts of the world and responsible for considerable economic losses. In this study, different types of paratuberculosis and MAP in sheep and goats were investigated in Inner Mongolia, a northern province in China contiguous with two countries and eight other provinces. A total of 4434 serum samples were collected from six cities in the western, central, and eastern regions of Inner Mongolia and analyzed using the ELISA test. In addition, tissue samples were collected from seven animals that were suspected to be infected with MAP. Finally, these tissues samples were analyzed by histopathological examination followed by polymerase chain reaction (PCR), IS1311 PCR-restriction enzyme analysis (PCR-REA), and a sequence analysis of five genes. Among all 4434 ruminant serum samples collected from the six cities in the western, central, and eastern regions of Inner Mongolia, 7.60% (337/4434) measured positive for the MAP antibody. The proportions of positive MAP antibody results for serum samples collected in the western, central, and eastern regions were 5.10% (105/2058), 6.63% (85/1282), and 13.44% (147/1094), respectively. For the seven suspected infected animals selected from the herd with the highest rate of positivity, the gross pathology and histopathology of the necropsied animals were found to be consistent with the pathological features of paratuberculosis. The PCR analysis further confirmed the diagnosis of paratuberculosis. The rest of the results demonstrated that herds of sheep and goats in Inner Mongolia were infected with both MAP type II and type III. To the best of our knowledge, this is the first study of the two subtypes of MAP strains in sheep and goats in Inner Mongolia.

Vitamin B and Vitamin C Affect DNA Methylation and Amino Acid Metabolism in Mycobacterium bovis BCG.

Vitamins are essential nutrients and key cofactors of enzymes that regulate cellular metabolism, and also activate the immune system. Recent studies have shown that vitamin B1 (VB 1) and vitamin C (Vc) can inhibit Mycobacterium tuberculosis growth, but the precise mechanism is still not well understood. In the present study, we have used RNA-sequencing (RNA-seq), liquid chromatography coupled to mass spectrometry (LC-MS) and single-molecule real-time (SMRT) sequencing to analyze the transcriptional, metabolic and methylation profiles of Mycobacterium bovis BCG when treated with VB 1 and Vc. Our results show that, after vitamin treatment, variant metabolites were mainly clustered in pathways related to amino acid metabolism. Treatment with both vitamins significantly up-regulated the gene encoding cysteine synthase A. Additionally, only BCG that was treated with VC showed m4c modifications. Genes harboring this methylation were up-regulated, suggesting that m4c methylation can promote gene transcription to some extent. Overall, this study contributes to the understanding of the effects of VB 1 and VC, and suggests that these vitamins constitute potential anti-tuberculosis drugs.

Rv3091, An Extracellular Patatin-Like Phospholipase in Mycobacterium tuberculosis, Prolongs Intracellular Survival of Recombinant Mycolicibacterium smegmatis by Mediating Phagosomal Escape.

Patatin-like phospholipases (PLPs) are important virulence factors of many pathogens. However, there are no prevailing studies regarding PLPs as a virulence factor of Mycobacterium tuberculosis (Mtb). Analysis of Rv3091, a putative protein of Mtb, shows that it belongs to the PLPs family. Here, we cloned and expressed the rv3091 gene in Mycobacterium smegmatis and, subsequently, conducted protein purification and characterization. We show that it possesses phospholipase A1, phospholipase A2, and lipase activity. We confirm the putative active site residues, namely, Ser214 and Asp407, using site directed mutagenesis. The Rv3091 is an extracellular protein that alters the colony morphology of M. smegmatis. The presence of Rv3091 enhances the intracellular survival capability of M. smegmatis in murine peritoneal macrophages. Additionally, it promotes M. smegmatis phagosomal escape from macrophages. Moreover, Rv3091 significantly increased the survival of M. smegmatis and aggravated lesions in C57BL/6 J murine lungs in vivo. Taken together, our results indicate that Rv3091 as an extracellular PLP that is critical to the pathogenicity of mycobacterium as it allows mycobacterium to utilize phospholipids for its growth and provides resistance to phagosome killing, resulting in its enhanced intracellular survival.

Characterization of a novel Mycobacterium tuberculosis serine protease (Rv3194c) activity and pathogenicity.

Mycobacterium tuberculosis (MTB) serine proteases are important pathogen-associated virulence factors that are involved in the invasion, bacterial persistence, and degradation of host defense factors. The current study identified and characterized a novel serine protease, Rv3194c, of MTB. A heterologous Rv3194c protein, purified from Escherichia coli, possessed proteolytic activity that could hydrolyze bovine serum albumin (BSA), milk, casein, and gelatin at an optimal temperature of 40 °C and a pH of 8.0. Furthermore, the divalent metal ions Ca2+ and Mn2+ increased the activity of Rv3194c. Betulinic acid, a Traditional Chinese Medicine (TCM) monomer; PMSF, a chemical inhibitor; and the Roche inhibitor cocktail inhibited proteolytic activity. Site-directed mutagenesis demonstrated that D308 and particularly S309 play a crucial role in the catalytic activity of Rv3194c protease. The cellular assays revealed that Rv3194c inhibits THP1-derived macrophage migration. Moreover, Rv3194c degraded the complement components, C3b and C5a, causing inhibition of phagocytosis and chemotaxis. In mice, Rv3194c enhanced the persistence of Mycobacterium smegmatis (Ms) in the lung, induced lung lesions, and promoted the release of inflammatory cytokines. The results of this study indicate that Rv3194c may play an important role in the pathogenicity of mycobacteria.

Extracellular Sphingomyelinase Rv0888 of Mycobacterium tuberculosis Contributes to Pathological Lung Injury of Mycobacterium smegmatis in Mice via Inducing Formation of Neutrophil Extracellular Traps.

Mycobacterium tuberculosis is the causative agent of tuberculosis (TB), which mainly causes pulmonary injury and tubercles. Although macrophages are generally considered to harbor the main cells of M. tuberculosis, new evidence suggests that neutrophils are rapidly recruited to the infected lung. M. tuberculosis itself, or its early secreted antigenic target protein 6 (ESAT-6), can induce formation of neutrophil extracellular traps (NETs). However, NETs trap mycobacteria but are unable to kill them. The role of NETs' formation in the pathogenesis of mycobacteria remains unclear. Here, we report a new M. tuberculosis extracellular factor, bifunctional enzyme Rv0888, with both nuclease and sphingomyelinase activities. Rv0888 sphingomyelinase activity can induce NETs' formation in vitro and in the lung of the mice and enhance the colonization ability of Mycobacterium smegmatis in the lungs of mice. Mice infected by M. smegmatis harboring Rv0888 sphingomyelinase induced pathological injury and inflammation of the lung, which was mainly mediated by NETs, induced by Rv0888 sphingomyelinase, associated protein (myeloperoxidase) triggered caspase-3. In summary, the study sheds new light on the pathogenesis of mycobacteria and reveals a novel target for TB treatment.

Targeting the gram-negative bacteria peptidoglycan synthase MraY as a new approach for monoclonal antibody anti-bacterial activity.

The use of antibiotics to target bacteria is a well-validated approach for controlling infections in animals and humans. Peptidoglycan biosynthesis is a crucial process in bacteria, and the conserved peptidoglycan synthase MraY is an attractive target for drug design. However, due to the lack of detailed MraY structural information, antibiotics targeting MraY have not yet been developed. In the present study, 2 hydrophilic regions of MraY from Escherichia coli were expressed as a fusion protein and used to raise a monoclonal antibody in mice. We confirmed that the MraY amino acid sequence PESHFSKRGTPT forms the core epitope recognized by the monoclonal antibody M-H11. Furthermore, our results show that M-H11 effectively controls Escherichia coli BL21 (DE3) plysS infection, both in vitro and in vivo. Our results may be of great value in the search for novel approaches used to control bacterial infections.

Characterization of Rv0888, a Novel Extracellular Nuclease from Mycobacterium tuberculosis.

Bacterial extracellular nucleases play important roles in virulence, biofilm formation, utilization of extracellular DNA as a nutrient, and degradation of neutrophil DNA extracellular traps. However, there is no current data available for extracellular nucleases derived from M. tuberculosis. Herein, we have identified and characterized Rv0888, an extracellular nuclease in M. tuberculosis. The protein was overexpressed in E. coli, and the purified Rv0888 protein was found to require divalent cations for activity, with an optimal temperature and pH of 41 °C and 6.5, respectively. Further results demonstrated that Rv0888 nuclease activity could be inhibited by four Chinese medicine monomers. Based on sequence analysis, Rv0888 nuclease exhibited no homology with any known extracellular nucleases, indicating that Rv0888 is a novel nuclease. Site-directed mutagenesis studies revealed that the H353, D387, and D438 residues play catalytic roles in Rv0888. In vivo infection studies confirmed that Rv0888 is required for infection and is related to pathogenicity, as the persistent ability of recombinant Mycobacterium smegmatis (rMS) Rv0888NS/MS and Rv0888S/MS is significantly higher than pMV262/MS in the lung tissue, and the Rv0888NS/MS and Rv0888S/MS could produce pathological changes in the mice lung. These results show that Rv0888 is relevant to pathogenicity of M. tuberculosis.

Identification and Characterization of Lipase Activity and Immunogenicity of LipL from Mycobacterium tuberculosis.

Lipids and lipid-metabolizing esterases/lipases are highly important for the mycobacterial life cycle and, possibly, for mycobacterial virulence. In this study, we expressed 10 members of the Lip family of Mycobacterium tuberculosis. Among the 10 proteins, LipL displayed a significantly high enzymatic activity for the hydrolysis of long-chain lipids. The optimal temperature for the lipase activity of LipL was demonstrated to be 37°C, and the optimal pH was 8.0. The lipase active center was not the conserved motif G-x-S-x-G, but rather the S-x-x-K and GGG motifs, and the key catalytic amino acid residues were identified as G50, S88, and K91, as demonstrated through site-directed mutagenesis experiments. A three-dimensional modeling structure of LipL was constructed, which showed that the GGG motif was located in the surface of a pocket structure. Furthermore, the subcellular localization of LipL was demonstrated to be on the mycobacterial surface by Western blot analysis. Our results revealed that the LipL protein could induce a strong humoral immune response in humans and activate a CD8+ T cell-mediated response in mice. Overall, our study identified and characterized a novel lipase denoted LipL from M. tuberculosis, and demonstrated that LipL functions as an immunogen that activates both humoral and cell-mediated responses.