Crystallographic structure of the PAS domain of the bacterial oxygen sensor protein fixL. The protein is depicted as a rainbow colored cartoon (N-terminus = blue, C-terminus = red while the heme ligand is shown as sticks (carbon = white, nitrogen = blue, oxygen = red, iron = orange).
The PAS domain is a protein domain contained in many signaling proteins where it functions as a signal sensor. PAS domains are found in a large number of organisms from bacteria to humans. The PAS domain was named after the three proteins in which it was first discovered:
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