Extracellular Proteins and Pathogenicity Networks

For the purposes of defining the structure of stimulons and regulons, transcrip-tomics provides a more complete picture than does proteomics, because - as already mentioned - many proteins still escape detection by gel-based proteomics. In many areas of application, however, proteomics can not be replaced by tran-scriptomics, because proteomics can also visualize events that never have been seen before by transcriptomics. Protein secretion is one such field of application that is crucial for Staphylococcus biology because of most of the virulence factors having signal sequences belong to the secretome. Using the dual channel technique it is possible to follow the protein secretion kinetics along the growth curve (Fig. 3.12). There are some proteins (e.g., SsaA, IsaA, Aly, Spa, SceD, LytM, and Aur) that are synthesized and secreted during exponential growth, but most are secreted only during the transient or even the stationary phase of growth [38, 39].

SarA, RNAIII, SaeR, ArlR, and others are key regulators involved in the expression of the majority of virulence genes whose products are required for host cell adhesion, for tissue invasion, or for tissue damage. The expression of these virulence proteins is regulated in a coordinated way, ensuring the expression of cell-surface-associated proteins during growth in a first step, followed by the expression of extracellular virulence proteins after settlement in the host in a second step [39-41]. Proteomics is again a highly sophisticated strategy by which to define the entire set of extracellular proteins controlled by these global virulence regula-

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