A globin-coupled oxygen sensor from the facultatively alkaliphilic Bacillus halodurans C-125

We have recently discovered heme-containing signal transducers from the arc haeon Halobacterium salinarum (HemAT-Hs) and the gram-positive bacterium Ba cillus subtilis (HemAT-Bs). These proteins bind diatomic oxygen and trigger aerotactic responses. We identified that HemAT oxygen-sensing domains cont ain a globin-coupled sensor (GCS) motif, which exists as a two-domain trans ducer, having no similarity to the PAS domain (Period circadian protein, Ah receptor nuclear translocator protein, Single-minded protein) superfamily transducers. Using the GCS motif, we predicted that a 439-amino-acid protei n annotated as a methyl-accepting chemotaxis protein (MCP) in the facultati vely alkaliphilic bacterium Bacillus halodurans is a globin-coupled oxygen sensor. We cloned, expressed, and purified GCS(Bh) and performed its spectr al analysis. GCS(Bh) binds heme and shows myoglobin-like spectra. This sugg ests that GCS(Bh) acts as an oxygen sensor and transmits a conformational s ignal through a linked signaling domain to trigger an aerotactic response i n B. halodurans.