coli HAK006 find more as reporter strain. Cells were grown in minimal media containing different K+ concentrations (10 mM and 0.2 mM) to the mid-exponential phase, β-galactosidase activity was determined, and is given in Miller Units . The data are average values obtained from at least three independent experiments, and error bars represent standard deviations. The enzymatic activities of the KdpD-Usp chimeras in vitro
To test whether the sensing capabilities of the KdpD-Usp chimeras were related to altered enzymatic activities, we determined the activities of autokinase-, KdpE-phosphotransferase-, and KdpE-phosphatase for each chimera (see Methods for details). All KdpD-Usp chimeras exhibited kinase and KdpE-phosphotransferase activity (Fig. 6A). KdpD has an ATP-dependent phosphatase activity, which is modulated
upon binding of ATP to the N-terminal KdpD-domain [9, 16]. The ATP-dependency of the phosphatase activity was not changed in any of the KdpD-Usp chimeras, because learn more significant dephosphorylation could only be observed in the presence of ATP (Fig. 6B). Despite detection of enzymatic activities for all chimeras, the ratio between kinase-phosphotransferase to phosphatase activities is important for the corresponding output (Table 1). The ratios for Salmocoli-KdpD, Agrocoli-KdpD and KdpD-UspA, KdpD-UspD, KdpD-UspF, KdpD-UspG were comparable to wild-type KdpD (deviation less than 20%). In KdpD-UspC and Streptocoli-KdpD, these ratios were shifted toward the OSI-027 mw kinase-phosphotransferase activity, resulting in higher levels of phosphorylated KdpE. The enhanced kdpFABC expression mediated by KdpD-UspC and Streptocoli-KdpD under K+ limitation can therefore be explained by decreased phosphatase activities (Fig. 6B). Pseudocoli-KdpD was characterized by a ratio that was drastically
shifted to the phosphatase activity, resulting in less phosphorylated KdpE. This result might explain Sitaxentan the low induction potential of this chimera in response to K+ limitation and salt stress. Remarkably, KdpD-UspF and KdpD-UspG were characterized by decreased phosphatase activities. Table 1 Kinase-phosphotransferase to phosphatase ratios of the KdpD chimeras. Chimera Kinase-phosphotransferase to phosphatase ratio KdpD 1.00 KdpD-UspA 0.81 KdpD-UspC 1.44 KdpD-UspD 0.89 KdpD-UspF 1.15 KdpD-UspG 1.00 Agrocoli-KdpD 0.78 Salmocoli-KdpD 0.83 Streptocoli-KdpD 1.44 Pseudocoli-KdpD 0.35 Figure 6 In vitro activities of the KdpD-Usp chimeras. KdpD-autokinase and KdpE-phosphotransferase activities (A) as well as KdpE-phosphatase activities (B) were determined as described in Methods. Data are presented as percentages of maximal accumulation of KdpD~P or KdpE~P (after 3 min, kinase as well as phosphotransferase activity) (A), respectively, or as percentages of the dephosphorylation initial rates relative to wild-type KdpD (+/- ATPγS) (B). For wild-type KdpD (100% values), the autophosphorylation activity of KdpD was determined with 14 pmol min-1 mg-1 protein.