Assembly of the Transmembrane Domain of E. coli PhoQ Histidine Kinase: Implications for Signal Transduction from Molecular Simulations
Figure 7
TM connectivity and implications for signaling mechanism.
The panels (A) and (B) indicate the projection for the F0 and F1 states, respectively, on the periplasmic (top) and cytoplasmic (bottom) surface of the membrane of the helical termini of the TM model. The contour lines represent the position of TM1 and TM2 during MD, and the dots represent the position of SD and HAMP available structures at the same section surface. (Central panel) At high mM concentration of Mg2+ and Ca2+ cations, metal bridges are formed between the SD acidic cluster and the negatively charged membrane. This conformation can be associated to the F0 state of our model and to a kinase-dominant state (K+). When the concentration decreases, the metal ion bridges are disrupted, leading to repulsion between the membrane and SD active site. This triggers a conformational change of the TM domain (F1 state associated to a phosphatase-dominant conformation, P+), and results in a rotation of TM2 at the cytoplasmic interface, that is then transmitted to the linked HAMP domain.