Proteins with one TMH were only considered as possible membrane proteins if the TMH region was positioned beyond the first 70 N-terminal amino acids. This was
done to avoid confusion with potential secreted proteins. Figure 3 Number of TMH regions in membrane proteins identified in the Triton X-114 lipid phase fraction of M. tuberculosis H37Rv. Number of identified proteins compared to the total number of predicted proteins is given. The white bars represent the total number of predicted membrane proteins in the genome based on the TMHMM algorithm version 2.0, while the black bars represent those observed in the present study. Lipoproteins Lipoproteins represent a subgroup of exported proteins characterized Galunisertib mw by the presence of a lipobox. The lipobox motif is located in the distal C-terminal part of the N-terminal signal peptide . This motif is a recognition signal for lipid modification on the conserved
and essential cysteine residue. KU55933 order Precursor lipoproteins are mainly translocated in a Sec-dependent manner across the plasma membrane and are subsequently modified . The proteins identified in this study were analysed by the lipoP algorithm http://www.cbs.dtu.dk/services/LipoP/, and 63 were predicted as potential lipoproteins (Additional file 2, Table S1) based on the presence of a cleavable signal peptide and a lipobox motif. Eight lipoproteins are described for the first time. In sum the findings comprises over 56% of all predicted lipoproteins in the genome. Outer membrane proteins learn more Outer membrane proteins (OMPs) are a class of proteins residing in the outer membrane of bacterial cells. Identification of OMPs is important as they are exposed on the bacterial surface
and so are accessible drug targets. Recently, Song and colleagues analysed the genome of M. tuberculosis and predicted 144 proteins as potential OMPs based on the amphilicity of the β-strand regions, absence of hydrophobic Methane monooxygenase α-helices and the presence of a signal peptide . In our study, we observed 54 (37.5%) of these proteins, and 9 of them have not been described in previous proteomic works (Additional file 2, Table S1). GRAVY The ‘grand mean of hydropathicity’ (GRAVY) score is the average hydropathy score for a protein. According to Kyte and Doolittle, integral membrane proteins have a higher GRAVY score than soluble proteins. A positive score >-0.4 suggests increased probability for membrane association; the higher the score, the greater the probability . GRAVY scores were calculated for all the identified proteins using the PROTPARAM tool http://us.expasy.org/tools/protparam.html. Three-hundred and sixty nine proteins without a TMH region had positive GRAVY scores (Additional file 3, Table S2).