Definition of novel cell envelope associated proteins in Triton X-114 extracts of Mycobacterium tuberculosis H37Rv

Abstract

BackgroundMembrane- and membrane-associated proteins are important for the pathogenicity of bacteria. We have analysed the content of these proteins in virulent Mycobacterium tuberculosis H37Rv using Triton X-114 detergent-phase separation for extraction of lipophilic proteins, followed by their identification with high resolution mass spectrometry.ResultsIn total, 1417 different proteins were identified. In silico analysis of the identified proteins revealed that 248 proteins had at least one predicted trans-membrane region. Also, 64 of the identified proteins were predicted lipoproteins, and 54 proteins were predicted as outer membrane proteins. Three-hundred-and-ninety-five of the observed proteins, including 91 integral membrane proteins were described for the first time. Comparison of abundance levels of the identified proteins was performed using the exponentially modified protein abundance index (emPAI) which takes into account the number of the observable peptides to the number of experimentally observed peptide ions for a given protein. The outcome showed that among the membrane-and membrane-associated proteins several proteins are present with high relative abundance. Further, a close examination of the lipoprotein LpqG (Rv3623) which is only detected in the membrane fractions of M. tuberculosis but not in M. bovis, revealed that the homologous gene in M. bovis lack the signal peptide and lipobox motif, suggesting impaired export to the membrane.ConclusionsAltogether, we have identified a substantial proportion of membrane- and membrane-associated proteins of M. tuberculosis H37Rv, compared the relative abundance of the identified proteins and also revealed subtle differences between the different members of the M. tuberculosis complex.

Mycobacterium tuberculosis acquires iron by cell-surface sequestration and internalization of human holo-transferrin

“…This observation is in accordance with previous results where it has been identified as a 43.6-kDa culture filtrate protein of M. bovis 41 and as a membrane-associated protein in M.tb H37Rv [42][43][44][45] . The presence of GAPDH and other glycolytic proteins on the surface of several prokaryotes and eukaryotic cells, despite the lack of a distinct secretory signal, has been referred to as 'nonclassical secretion' 46,47 and a bioinformaticsbased analysis of M.tb GAPDH failed to predict any secretion via the sec-dependent or twin arginine translocation system 41 .…”

General secretion signal for the mycobacterial type VII secretion pathway

“…Other proteins belong to the Pfam esxAB clan (37) and are therefore also putative secretion substrates. Another likely substrate is ESX-1-encoded EspJ, which was previously identified in M. tuberculosis cell envelope extracts (38). Finally, we also identified a T7S motif in EspB, one of the larger proteins secreted by ESX-1 (14).…”

Thiol-Dependent Peroxidases in Mycobacterium tuberculosis Antioxidant Defense

“…In M. tuberculosis, TPx was firstly characterized as an extracellular antigen that induces a strong proliferative response in animals (Weldingh et al, 1998) . MtTPx was repeatedly found in culture filtrates; it has also been found associated to membranes and in cytosolic fractions (Rosenkrands et al, 2000;Covert et al, 2001;Malen et al, 2007;Malen et al, 2010).…”