Emerging roles for thiol dioxygenases as oxygen sensors.

Dona M Gunawardana,Karen C Heathcote,Emily Flashman

doi:10.1111/febs.16147

Abstract

Cysteine dioxygenases, 3-mercaptopropionate dioxygenases and mercaptosuccinate dioxygenases are all thiol dioxygenases (TDOs) that catalyse oxidation of thiol molecules to sulphinates. They are Fe(II)-dependent dioxygenases with a cupin fold that supports a 3xHis metal-coordinating triad at the active site. They also have other, broadly common features including arginine residues involved in substrate carboxylate binding and a conserved trio of residues at the active site featuring a tyrosine important in substrate binding catalysis. Recently, N-terminal cysteinyl dioxygenase enzymes (NCOs) have been identified in plants (plant cysteine oxidases, PCOs), while human 2-aminoethanethiol dioxygenase (ADO) has been shown to act as both an NCO and a small molecule TDO. Although the cupin fold and 3xHis Fe(II)-binding triad seen in the small molecule TDOs are conserved in NCOs, other active site features and aspects of the overall protein architecture are quite different. Furthermore, the PCOs and ADO appear to act as biological O2 sensors, as shown by kinetic analyses and hypoxic regulation of the stability of their biological targets (N-terminal cysteine oxidation triggers protein degradation via the N-degron pathway). Here, we discuss the emergence of these two subclasses of TDO including structural features that could dictate their ability to bind small molecule or polypeptide substrates. These structural features may also underpin the O2 -sensing capability of the NCOs. Understanding how these enzymes interact with their substrates, including O2 , could reveal strategies to manipulate their activity, relevant to hypoxic disease states and plant adaptive responses to flooding.

Highlights

Thiol dioxygenases (TDOs) have been known for many decades as having important roles in cysteine catabolism, taurine metabolism and other small molecule thiol turnovers
Tyr157 plays a important role in Cysteine dioxygenase (CDO) substrate binding, so this role could be fulfilled by other Tyr residues in the active sites of N-terminal cysteinyl dioxygenase (NCO), distinct modes of primary substrate binding between the two classes of TDO seem likely, especially as there is no equivalent in NCOs to the interaction between Arg residues and substrate carboxylate groups seen in CDOs, 3-mercaptopropionic acid dioxygenase (3MDO) and mercaptosuccinate dioxygenase (MSDO)
As plant cysteine oxidase (PCO):substrate interactions are likely to occur across a greater surface area of the enzyme than is the case for small molecule TDOs, it was interesting to find that the position of a C-terminal loop in the AtPCO substrate-free structures creates an open tunnel-like cavity leading to the active site (Fig. 1CII) [5]

Summary

Introduction

Thiol dioxygenases (TDOs) have been known for many decades as having important roles in cysteine catabolism, taurine metabolism and other small molecule thiol turnovers. While CDO shares these conserved structural features (Fig. 1AI), its active site Fe (II) coordination is different to that of other cupin superfamily enzymes.

Results

Conclusion