Crystal structures of the CO and NOBound DosS GAF-A domain and implications for DosS signaling in Mycobacterium tuberculosis

- M. tuberculosis DosS is a gas sensor that controls entry into the latent state.
- DosS autophosphorylation occurs in the Fe(II)CO and NO, but not Fe(II)O2, states.
- DosS has a heme in the GAF-A domain 200 amino acids from the autophosphorylation site.
- The active GAF-A conformations differ from that of the inactive Fe(III) state.
- The crystal structures favor a conformational equilibrium signaling mechanism.

DosS is a sensor in Mycobacterium tuberculosis that differentially responds to O2, NO, and CO, as well as to changes in the redox state of the prosthetic heme iron atom. The ferrous protein and its Fe(II)NO and Fe(II)CO complexes undergo autophosphorylation and subsequently transfer the phosphate group to DosR, a nuclear factor, to activate it. In contrast, autophosphorylation is negligible with the ferric protein and the Fe(II)O2 complex. To clarify the basis for this differential response to gases, we have determined the crystal structures of the NO and COcomplexes of the DosS GAF-A domain, which contains the heme to which the gases bind. Comparison of these crystal structures with those reported for the phosphorylation-inactive ferric GAF-A domain suggest that the GAF-A domain is in a dynamic equilibrium between active and inactive states, and that the position of Glu87 in the heme cavity, which depends on the which gas is bound, acts as a modulator of the equilibrium, and therefore of catalytic activity.

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