A complementary approach is to study the total protein complement, or 'proteome', of the bacterium at different stages of the growth cycle. Proteins are isolated then separated by electrophoresis in two dimensions, firstly by isoelectric focusing and thereafter by molecular mass, to yield a characteristic pattern of spots after staining (Urquhart et al 1997). The individual protein in each spot may be isolated and identified by accurately determining its mass in a spectrometer either directly, or following trypsin digestion and sizing of the resulting fragments. Reference to a database of predicted protein molecular weights generated from the mycobacterial genome sequence would tell which protein is present in the spot. If the protein appears not to be in the predicted set, techniques such as tandem nanoelectrospray mass spectrometry yield sequence data from which the protein may be identified. This technique is particularly useful for detecting and analysing post-translational modifications such as glycosylation (M. Ward, W. Blackstock, M.-P. Gares, D. B. Young & C. Abou-Zeid, unpublished work 1997).
In summary, the availability of the genome sequence of M. tuberculosis is providing many benefits in the search for new drugs to treat tuberculosis. The efficiency and speed with which targets may be identified increases the likelihood that novel potent leads will be found, which may then be developed into the next generation of antituberculosis drugs. Furthermore, new approaches may be followed, thereby increasing the diversity of targets that are available for study.
I acknowledge the contribution many people have made to the strategy outlined in this article, including colleagues at Glaxo Wellcome, Gavin Chung, Martin Everett, Karen Kempsell, Pauline Lukey, Ruth McAdam, Steve Martin and Paul Smith, and many academic collaborators participating in the Action TB Initiative.
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