The contributions of change and conservation in Spo0 protein specificity to pathway remodeling.

Cross-species phosphotransfer profiling probes the relative positions of Spo0 pathway specificity spectra across architectures. Horizontal axis represents phosphodonor specificity signatures, as in Fig 2. Vertical lines connect points corresponding to the same phosphodonor. (A) Schematic showing the positions of receiver specificity spectra in interaction space under the hypothesis that pathway remodeling arose via changes in kinase specificity. The Spo0A specificity spectra are similarly positioned in both architectures. This hypothesis predicts that every kinase that directly phosphorylates Spo0A in its native environment (filled circles) will also be capable of heterologous phosphorylation of Spo0A proteins from phosphorelays (open circles). (B) Positions of receiver specificity spectra under the hypothesis that pathway remodeling arose via changes in the Spo0A specificity spectrum. This hypothesis predicts the following heterologous interactions (open circles): Every direct phosphorylation kinase interacts with Spo0F proteins from phosphorelays and every phosphorelay kinase interacts with Spo0A proteins associated with direct phosphorylation architectures. (C) Receiver specificity spectra in the B. subtilis phosphorelay, the D. acetoxidans phosphorelay, and the C. acetobutylicum direct phosphorylation architectures. The relative positions of these spectra were inferred from experimentally determined autologous (filled circles) and heterologous (crossed open circles) interactions (summarized in Table 3; see also Figs 6, 8 and 9). The observed interactions support the hypothesis that pathway remodeling arose primarily through changes in kinase specificity, as shown in (A), with a minor shift in the Spo0A specificity spectrum of D. acetoxidans.