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Ultrafast dynamics of heme distortion in the O2-sensor of a thermophilic anaerobe bacterium
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Ultrafast dynamics of heme distortion in the O2-sensor of a thermophilic anaerobe bacterium
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Ultrafast dynamics of heme distortion in the O2-sensor of a thermophilic anaerobe bacterium
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Journal Article
Ultrafast dynamics of heme distortion in the O2-sensor of a thermophilic anaerobe bacterium
2021
Overview
Heme-Nitric oxide and Oxygen binding protein domains (H-NOX) are found in signaling pathways of both prokaryotes and eukaryotes and share sequence homology with soluble guanylate cyclase, the mammalian NO receptor. In bacteria, H-NOX is associated with kinase or methyl accepting chemotaxis domains. In the O
2
-sensor of the strict anaerobe
Caldanaerobacter tengcongensis
(
Ct
H-NOX) the heme appears highly distorted after O
2
binding, but the role of heme distortion in allosteric transitions was not yet evidenced. Here, we measure the dynamics of the heme distortion triggered by the dissociation of diatomics from
Ct
H-NOX using transient electronic absorption spectroscopy in the picosecond to millisecond time range. We obtained a spectroscopic signature of the heme flattening upon O
2
dissociation. The heme distortion is immediately (<1 ps) released after O
2
dissociation to produce a relaxed state. This heme conformational change occurs with different proportions depending on diatomics as follows: CO < NO < O
2
. Our time-resolved data demonstrate that the primary structural event of allostery is the heme distortion in the
Ct
H-NOX sensor, contrastingly with hemoglobin and the human NO receptor, in which the primary structural events are respectively the motion of the proximal histidine and the rupture of the iron-histidine bond.
Dioxygen protein sensors undergo structural distortions upon binding, but the role of heme distortion in allostery is unclear. Here heme distortion in a bacterial dioxygen sensor is studied using picosecond time-resolved electronic absorption spectroscopy and shown to control the allosteric equilibrium.
