Ultrafast dynamics of heme distortion in the O2-sensor of a thermophilic anaerobe bacterium

Olga N Petrova,Michel Negrerie,Byung-Kuk Yoo,Pierre Nioche,Isabelle Lamarre,Julien Selles

doi:10.1038/s42004-021-00471-9

Abstract

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 O2-sensor of the strict anaerobe Caldanaerobacter tengcongensis (Ct H-NOX) the heme appears highly distorted after O2 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 O2 dissociation. The heme distortion is immediately (<1 ps) released after O2 dissociation to produce a relaxed state. This heme conformational change occurs with different proportions depending on diatomics as follows: CO < NO < O2. 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.

Highlights

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 nitric oxide (NO) receptor
Ct H-NOX sensor binds the three diatomics NO, CO, and O213,16, it was proposed to act as an O2-sensor rather than a NO-sensor[17], especially since the Ct H-NOX domain is fused to a methylaccepting chemotaxis domain in a full-length protein[3]
The spectral evolution triggered by photodissociation of diatomics described here has never been observed previously in other O2-binding heme proteins, for which a positive induced absorption was always measured upon O2 dissociation (Supplementary Table S3), contrarily to Ct H-NOX

Summary

Introduction

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. A subfamily of H-NOX sensors found in facultative anaerobes (such as Shewanella oneidensis and Vibrio cholerae) are specific NO sensors that do not form a stable complex with O2 with sGC The function of such bacterial H-NOX proteins is thought to regulate biofilm formation or quorum sensing signaling in a NOdependent manner[9,10]. Ct H-NOX sensor binds the three diatomics NO, CO, and O213,16, it was proposed to act as an O2-sensor rather than a NO-sensor[17], especially since the Ct H-NOX domain is fused to a methylaccepting chemotaxis domain in a full-length protein[3] This presumed function of the Ct H-NOX is not yet demonstrated by in vitro assays in correlation with bacteria living conditions, as performed for example in the case of the NO-transporter cytochrome c’18. The tensed state of the heme is reached after O2 binding in

Methods

Results

Conclusion