Knowledge of virulence factors is important to understand the microbial pathogenesis and find better antibiotics. Mammalian cell entry (mce) is a crucial protein family for the virulence of Mycobacterium tuberculosis (M. tuberculosis). This review summarized the advances on mce genes. The genomic organization, characteristics of mce genes, phylogeny of this family, and their roles in M. tuberculosis virulence are emphasized in this review.

Mammalian cell entry gene family of Mycobacterium tuberculosis

A severe re-emergingzoonosis, leptospirosis, is caused by pathogenic spirochetes of the genus Leptospira. Several studies have identified leptospiral surface proteins with the ability to bind ECM and plasma components, which could mediate adhesion and invasion through the hosts. It has been shown that Mce of pathogenic Leptospira spp. is an RGD (Arg-Gly-Asp)-motif-dependent virulence factor, responsible for infection of cells and animals. In the present article, we decided to further study the repertoire of the Mce activities in leptospiral biological properties. We report that the recombinant Mce is a broad-spectrum ECM-binding protein, capable of interacting with laminin, cellular and plasma fibronectin and collagen IV. Dose--r-esponse interaction was observed for all the components, fulfilling ligand--receptor requirements. Mce is a PLG binding protein capable to recruit this component from NHS, generating PLA in the presence of PLG activator. Binding of Mce was also observed with the leukocyte cell receptors αLβ2 [(CD11a/CD18)-LFA-1] and αMβ2 [(CD11b/CD18)-Mac-1], suggesting the involvement of this protein in the host immune response. Indeed, virulent Leptospira L1-130 was capable of binding both integrins, whereas culture-attenuated M-20 strain only bind to αMβ2 [(CD11b/CD18)-Mac-1]. To the best of our knowledge, this is the first work to describe that Mce surface protein could mediate the attachment of Leptospira interrogans to human cell receptors αLβ2(CD11a/CD18) and αMβ2(CD11b/CD18).

Mammalian cell entry (Mce) protein of Leptospira interrogans binds extracellular matrix components, plasminogen and β2 integrin.

Cholesterol is important for the growth and persistence of Mycobacterium tuberculosis in macrophages. The mce4 locus, which is conserved in both M. tuberculosis and Mycobacterium bovis, is thought to be responsible for cholesterol transport into the bacteria. However, the exact roles of specific genes within the sophisticated mce4 system remain poorly understood. In this study, Mce4A and Mce4E of M. bovis, two proteins that are encoded by the mce4 locus, were expressed in Mycobacterium smegmatis. The recombinant strain expressing the Mce4E protein (M. smeg::E) performed better than that expressing the Mce4A protein (M. smeg::A) in a minimal medium with and without glycerol or cholesterol, which may be the reason why M. smeg::E showed better survival in ANA-1 macrophages than did M. smeg::A. Cytokine expression profiles were similar in macrophages infected with either recombinant strain. We also investigated the role of CD36 in recognizing Mce4A and Mce4E proteins. However, CD36 did not appear to be specif...

Comparative Study of the Growth and Survival of Recombinant Mycobacterium smegmatis Expressing Mce4A and Mce4E from Mycobacterium bovis

Mammalian cell entry (MCE) domains are so called due to the reported ability of an Escherichia coli strain harbouring the mce1 gene from Mycobacterium tuberculosis to invade mammalian cells. Bioinformatic analyses presented here demonstrated that proteins containing a single MCE domain are widespread in bacteria and that proteins containing multiple MCE domains are specific to and have evolved within Proteobacteria. Gene neighbourhood analyses revealed that MCE domain containing proteins are components of transporters and that multi MCE domain containing proteins constitute a novel type of transporter. E. coli was shown to harbour three MCE proteins: the single MCE domain protein MlaD and two multi-domain proteins PqiB and YebT. All three proteins were shown to locate to the inner membrane and bind phospholipids. Phenotypic studies revealed that their functions overlap but are distinct. Infection studies with Salmonella showed that the proteins are important for systemic infection but are not required for mammalian cell entry. Phospholipid growth experiments with Salmonella demonstrated that they are important for phospholipid uptake. These findings suggest that MCE domain containing proteins in Proteobacteria are not directly involved in mammalian cell entry and instead play a role in other aspects of mammalian infection related to phospholipid trafficking.

A role for proteobacterial mammalian cell entry domains in phospholipid trafficking and infection

Post-translational modifications (PTMs) could influence many aspects of protein behavior and function in organisms. Protein glycosylation is one of the major PTMs observed in bacteria, which is crucial for functional regulations of many prokaryotic and eukaryotic organisms. Mycobacterium bovis bacillus Calmette-Guerin (BCG) vaccine has been recognized as an indispensable tool in the global fight against tuberculosis (TB) worldwide over several decades. Nevertheless, analysis of glycoprotein profiles of BCG has not been clearly investigated. In this study, we performed O-mannosylated protein analysis in BCG bacteria using gel-based and gel-free approaches. In total, 1,670 hexosylated peptides derived from 754 mannosylated proteins were identified. Furthermore, twenty novel protein products supported by 78 unique peptides not annotated in the BCG database were detected. Additionally, the translational start sites of 384 proteins were confirmed, and 78 proteins were validated through the extension of translational start sites based on N-terminus-derived peptides. The bioinformatic analysis of the O-mannosylated proteins was performed and the expression profiles of four randomly selected proteins were validated through Western blotting. A number of proteins involved in metabolic pathways, including the tricarboxylic acid cycle, glycolysis, oxidative phosphorylation and two-component system, are discussed. Taken together, these results offer the first O-mannosylated protein analysis of a member of mycobacteria reported to date by using complementary gel-based and gel-free approaches. Some of the proteins identified in this study have important roles involved in metabolic pathways, which could provide insight into the immune molecular mechanisms of this recognized vaccine strain. This article is protected by copyright. All rights reserved.

Characterization of O-mannosylated proteins profiling in bacillus Calmette-Guérin via gel-based and gel-free approaches

CONTEXTE : De nombreuses donnees de recherches ont confirme que les proteines d'entree des cellules des mammiferes (Mce) sont en relation avec la virulence de la tuberculose. OBJECTIF: Pour obtenir des informations sur l'effet de la proteine de la famille Mce sur la pathogenese de Mycobacterium bovis, nous avons exprime la proteine recombinante Mce4E dans Escherichia coli et investigue dans l'etude actuelle son effet sur l'expression de tumor necrosis factor alpha (TNF-a), de NO inducible (iNO), de l'interleukin 6 (IL-6) et de l'interleukin 12 (IL-12) dans les macrophages alveolaires au moyen de la reverse transcriptase reaction polymerase en chaine (PCR-RT) en temps reel. RESULTATS: Notre etude a demontre que dans les macrophages alveolaires apres stimulation pendant 48 h par la proteine Mce4E, l'expression de la TNF-a est stimulee avec une augmentation du niveau de IL-6 mRNA (P < 0,05), mais qu'aucun changement de l'expression de IL-12 ne survient dans les macrophages. En plus des modifications du profil d'expression des cytokines dans les macrophages, il y a une reduction de l'expression de l'iNOS (P < 0,05). Notre analyse de la MTT [3, (4,5 dimethylthiazol2yl)-2,5 diphenyl-tetrazolium bromide] dans le macrophage a demontre egalement que la proteine Mce4E pouvait inhiber l'activite macrophagique. CONCLUSION: Nos donnees suggerent que les proteines Mce4E peuvent induire une reponse inflammatoire de l'hote a l'egard de M. bovis et peuvent jouer un role important dans les interactions entre l'hote et l'agent pathogene.

Mycobacterium bovis Mce4E protein may play a role in modulating cytokine expression profile in alveolar macrophage.

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Mycobacterium bovis Mce4E protein may play a role in modulating cytokine expression profile in alveolar macrophage.