Membrane and membrane-associated proteins in Triton X-114 extracts of Mycobacterium bovis BCG identified using a combination of gel-based and gel-free fractionation strategies

Tuberculosis is an ancient disease that remains a significant global health problem. Because many membrane and membrane-associated proteins of this pathogen represent potential targets for drugs, diagnostic probes or vaccine components, we have analysed Mycobacterium bovis, bacillus Calmette-Guérin (BCG) substrain Moreau, using Triton X-114 for extraction of lipophilic proteins, followed by identification with LC coupled MS/MS. We identified 351 different proteins in total, and 103 (29%) were predicted as integral membrane proteins with at least one predicted transmembrane region and another 84 (23.9%) proteins had a positive grand average of hydropathicity (GRAVY) value, indicating increased probability for membrane association. Altogether 43 predicted lipoproteins (Lpps) were identified which is close to 50% of the total number of Lpps in the genome. Fifty-four proteins, including twenty-four predicted integral membrane proteins and seven predicted Lpps are described for the first time. The proportion of hydrophobic membrane and membrane-associated proteins shows that Triton X-114 is a highly efficient method for extraction of membrane proteins from bacteria, without the need for preisolation of membranes. ATP synthase, NAD(P) transhydrogenase, ubiquinone oxidoreductase and ubiquinol-cytochrome C reductase appear to represent major enzyme complexes in the membrane of Mycobacterium tuberculosis complex organisms.