Interaction of a Mycobacterium tuberculosis repetitive DNA sequence with eukaryotic proteins

Is there an emerging endosymbiotic relationship between mycobacteria and the human host based on horizontal transfer of genetic sequences?

While not negating the seriousness of tuberculosis and the need to prevent and combat the disease effectively, the large percentage of infected, apparently healthy individuals who harbour latent infections warrants consideration whether an endosymbiotic relationship is being established between mycobacteria and man. By means of a gene decay process eliminating their most metabolically important pathogenic genes associated with an increasing need for host gene products during prolonged intracellular survival, mycobacteria appears to be undergoing a process of establishing a less dangerous relationship with its host. To have tolerated this relationship over time, humans must have benefited. This is suggested to have occurred via changes in DNA higher order structure altering combinatorially regulated gene expression allowing increased cerebrodiversity. It can be expected that, beyond a certain threshold, negative effects ensued, leading to neuropathology and increased susceptibility for certain psychiatric disorders. These processes have probably been happening since the earliest contact with mycobacteria, but recently may have become modified by the emergence of epidemic tuberculosis and waves of increased oxidative stress following the circumstances associated with the Industrial Revolution and the more recent AIDS pandemic. The organism seems to have uniquely exploited the normal stress reaction of the host. Genomic stresses include changes associated with glucocorticoid effects as well as upregulated reactive oxygen species and stress/(heat shock) protein production, the latter two of which result in host cell cycle delay. Subsequently replication dependent chromosomal fragile sites appear in the host genome and together with upregulated chaperonins and mobile element activation, the scene is set for sequence exchange between the organism and host. If proven, these events raise the possibility of modifying chromatin epigenetically to retain the proposed advantages while silencing pathogenicity factors.

Identifying putative Mycobacterium tuberculosis Rv2004c protein sequences that bind specifically to U937 macrophages and A549 epithelial cells

Virulence and immunity are still poorly understood in Mycobacterium tuberculosis. The H37Rv M. tuberculosis laboratory strain genome has been completely sequenced, and this along with proteomic technology represent powerful tools contributing toward studying the biology of target cell interaction with a facultative bacillus and designing new strategies for controlling tuberculosis. Rv2004c is a putative M. tuberculosis protein that could have specific mycobacterial functions. This study has revealed that the encoding gene is present in all mycobacterium species belonging to the M. tuberculosis complex. Rv2004c gene transcription was observed in all of this complex's strains except Mycobacterium bovis and Mycobacterium microti. Rv2004c protein expression was confirmed by using antibodies able to recognize a 54-kDa molecule by immunoblotting, and its location was detected on the M. tuberculosis surface by transmission electron microscopy, suggesting that it is a mycobacterial surface protein. Binding assays led to recognizing high activity binding peptides (HABP); five HABPs specifically bound to U937 cells, and six specifically bound to A549 cells. HABP circular dichroism suggested that they had an alpha-helical structure. HABP-target cell interaction was determined to be specific and saturable; some of them also displayed greater affinity for A549 cells than U937 cells. The critical amino acids directly involved in their interaction with U937 cells were also determined. Two probable receptor molecules were found on U937 cells and five on A549 for the two HABPs analyzed. These observations have important biological significance for studying bacillus-target cell interactions and implications for developing strategies for controlling this disease.

Characterising Mycobacterium tuberculosis Rv1510c protein and determining its sequences that specifically bind to two target cell lines

The process of Mycobacterium tuberculosis infection of the macrophage implies a very little-known initial recognition and adherence step, important for mycobacterial survival; many proteins even remain like hypothetical. The Rv1510c gene, encoding a putatively conserved membrane protein, was investigated by analysing the M. tuberculosis genome sequence data reported by Cole et al. and a previous report that used PCR assays to show that the Rv1510 gene was only present in M. tuberculosis. This article confirmed all the above and identified the transcribed gene in M. tuberculosis, Mycobacterium africanum, and in M. tuberculosis clinical isolates. Antibodies raised against peptides from this protein recognised a 44 kDa band, corresponding to Rv1510c theoretical mass (44,294 Da). Assays involving synthetic peptides covering the whole protein binding to U937 and A549 cell lines led to recognising five high activity binding peptides in the Rv1510 protein: 11094, 11095, 11105, 11108, and 11111. Their affinity constants and Hill coefficients were determined by using U937 cells. Cross-linking assays performed with some of these HABPs showed that they specifically bound to a U937 cell line 51 kDa protein, but not to Hep G2 or red blood cell proteins, showing this interaction's specificity.