The mpn668 gene of Mycoplasma pneumoniae encodes a novel organic hydroperoxide resistance protein.

Mycoplasma pneumoniae (M. pneumoniae), as an obligate parasite, has evolved a protective strategy for coping with oxidative challenges caused by M. pneumoniae itself as well as the host immune system. However, to date, few antioxidant enzymes have been identified in mycoplasmas. In this report, we identified a protein encoded by the mpn668 gene from M. pneumoniae with a putative function as an organic hydroperoxide reductase (Ohr). The results indicated that the recombinant 140 amino acid protein, designated rMPN668, displayed hydroperoxidase activity towards both organic (tert-butyl hydroperoxide) and inorganic (hydrogen peroxide) hydroperoxides in the presence of a reducing agent such as dithiothreitol. Moreover, the expression of mpn668 in M. pneumoniae is upregulated in response to oxidative stress. Additionally, homology modeling of MPN668 and a molecular dynamics simulation suggest that both Cys55 and Cys119 form part of the active site of the protein. Mutants in which Cys55 or Cys119 were replaced with a serine lack antioxidant activity, indicating that MPN668 is a Cys-based peroxidase, consistent with it representing a new member of the Ohr family.

Hypothetical protein Cpn0423 triggers NOD2 activation and contributes to Chlamydia pneumoniae-mediated inflammation.

BACKGROUND: Chlamydia pneumoniae (C. pneumoniae) is pathogenic to humans, by causing pulmonary inflammation or bronchitis in both adolescents and young adults. However, the molecular signals linking C. pneumoniae components to inflammation remain elusive. This study was to investigate the effect of Chlamydia-specific Cpn0423 of C. pneumoniae on C. pneumoniae-mediated inflammation. RESULTS: Cpn0423 was detected outside of C. pneumoniae inclusions, which induced production of several cytokines including macrophage inflammatory protein-2 (MIP-2) and interleukins (ILs). Production of the Cpn0423-induced cytokines was markedly reduced in cells pretreated with NOD2-siRNA, but not with negative control oligonucleotides. Mice treated with Cpn0423 through intranasal administration exhibited pulmonary inflammation as evidenced by infiltration of inflammatory cells, increased inflammatory scores in the lung histology, recruitment of neutrophils and increased cytokines levels in the BALF. CONCLUSION: Cpn0423 could be sensed by NOD2, which was identified as an essential element in a pathway contributing to the development of C. pneumoniae -mediated inflammation.

Mycoplasma lipoproteins and Toll-like receptors.

Mycoplasmas, the smallest free-living, self-replicating bacteria with diameters of 200 to 800 nm, have been reported to be associated with human diseases. It is well known that the mycoplasma lipoprotein/peptide is able to modulate the host immune system, whose N-terminal structure is an important factor in inducing immunity and distinguishing Toll-like receptors (TLRs). However, there is still no clear elucidation about the pathogenic mechanism of mycoplasma lipoprotein/peptide and the signaling pathway. Some researchers have focused on understanding the structures of these proteins and the relationships between their structure and biological function. This review provides an update on the research in this field.

[Mycoplasma genitalium lipid-associated membrane proteins induce human monocytic cell express proinflammatory cytokines and apoptosis by activating nuclear factor kappaB].

Designed to investigate the potential pathogenicity of Mycoplasma genitalium (M. genitalium) and its molecular mechanisms responsible for the induction of proinflammatory cytokines gene expression in human monocytic cells (THP-1) stimulated by lipid-associated membrane proteins (LAMPs) prepared from M. genitalium. THP-1 cells were stimulated with LAMPs to analyze the production of proinflammatory cytokines and the expression of mRNA was detected by RT-PCR. Cell apoptosis was detected in THP-1 cells by Annexin V-propidium iodide staining. The activity of transcriptional factors, NF-kappaB, was examined in THP-1 cells treated with LAMPs by EMSA. The effects of pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-kappaB, on the production of proinflammatory cytokines, the expression of mRNA and apoptosis were also examined in THP-1 cells treated with LAMPs. M. genitalium LAMPs stimulate THP-1 cells to produce TNF-alpha, IL-1beta and IL-6 in dose- and time-dependent manner. The mRNA levels and cell apoptosis are also downregulated in response to LAMPs stimulation and inhibited by PDTC treatment. M. genitalium LAMPs are found to trigger NF-kappaB activation, a possible mechanism for the induction of mRNA expression and the cell apoptosis. This study demonstrated that M. genitalium may be an important etiological factor of certain disease due to the ability of LAMPs to stimulated the expression of mRNA and apoptosis, which is probably mediated through the activation of NF-kappaB.

Interactions between mycoplasma lipid-associated membrane proteins and the host cells.

Mycoplamas are a group of wall-less prokaryotes widely distributed in nature, some of which are pathogenic for humans and animals. There are many lipoproteins anchored on the outer face of the plasma membrane, called lipid-associated membrane proteins (LAMPs). LAMPs are highly antigenic and could undergo phase and size variation, and are recognized by the innate immune system through Toll-like receptors (TLR) 2 and 6. LAMPs can modulate the immune system, and could induce immune cells apoptosis or death. In addition, they may associate with malignant transformation of host cells and are also considered to be cofactors in the progression of AIDS.