Differences in the Second Coordination Sphere Tailor the Substrate Specificity and Reactivity of Thiol Dioxygenases

Abstract

substrate analogue selenocysteine (Sec)-bound forms of CDO in the Fe(II) and Fe(III) states were investigated spectroscopically. Despite the identical binding modes of Cys and Sec, CDO was found to be unable to oxidize Sec.

Spectroscopic, electrochemical, and kinetic trends in Fe(III)–thiolate disproportionation near physiologic pH

“…Mononuclear non-heme Fe enzymes are diverse and ubiquitous with functionality broadly divided into oxygen or substrate activation [ 1 – 3 ]. Thiol dioxygenases, such as cysteine dioxygenase (CDO) and cysteamine dioxygenase (ADO), transform biologic thiols into sulfinates and are the largest family of non-heme Fe(II)-dependent enzymes in which Fe is bound to the protein by a histidine triad [ 1 , 4 – 11 ].…”

“…Mononuclear non-heme Fe enzymes are diverse and ubiquitous with functionality broadly divided into oxygen or substrate activation [ 1 – 3 ]. Thiol dioxygenases, such as cysteine dioxygenase (CDO) and cysteamine dioxygenase (ADO), transform biologic thiols into sulfinates and are the largest family of non-heme Fe(II)-dependent enzymes in which Fe is bound to the protein by a histidine triad [ 1 , 4 – 11 ]. Given the ubiquity and importance in nature of thiol dioxygenases, including CDO, ADO, and plant cysteine dioxygenase (PCO), the Pfam-defined CDO_I family and PCO_ADO family have received increasing attention to better understand their structures and functions [ 1 , 3 , 6 , 12 – 15 ].…”

Spectroscopic, Electrochemical, and Kinetic Trends in Fe(III)–Thiolate Disproportionation Near Physiological pH

“…Thiol dioxygenases, such as cysteine dioxygenase (CDO) and cysteamine dioxygenase (ADO), transform biological thiols into sulfinates through the activation of molecular oxygen. [1][2][3][4][5][6][7][8][9] Thiol dioxygenase active sites feature a mononuclear, non-heme Fe center bound by three histidine residues forming a facial 3N binding mode (Figure 1). The remaining three coordination sites on Fe are either occupied by three water molecules in the absence of substrate or by a combination of thiol substrate, water, or dioxygen.…”

“…[12] In contrast, evidence strongly suggests monodentate substrate binding at the ADO active site. [4,9,13,14] When compared to CDO and MDO, ADO is unique in its substrate binding mode and scope. Cysteine is bound to CDO in a bidentate mode while ADO contains no substrate.…”

A Nonheme Iron(III) Superoxide Complex Leads to Sulfur Oxygenation

“…The activation of dioxygen by nonheme iron enzymes is critical to a range of biological processes. − One such class of nonheme iron enzymes are the thiol dioxygenases (TDOs), which convert thiol substrates into S-oxygenated compounds and are found in a wide range of organisms, from bacteria, , to plants, , to mammals. , The TDOs play critical roles in biochemical processes, − and their misfunctioning has been implicated in neurodegenerative diseases, , autoimmune disorders, , and cancer. − The TDOs utilize a mononuclear iron center bound by an unusual 3-His structural motif, as opposed to the canonical 2-His-1-carboxylate iron site found in other nonheme iron enzymes. − Despite their widespread biochemical significance, the mechanism of S-oxygenation for TDOs remains poorly understood. − For example, two hypothetical mechanisms have been proposed for cysteine dioxygenase (Scheme ), a mammalian TDO that converts cysteine to cysteine sulfinate. ,− However, experimental evidence for either mechanism remains scarce. − In synthetic systems, significant efforts have been made to bind and activate O 2 with nonheme iron complexes. − These efforts have yielded only three examples of Fe­(O 2 ) adducts, and none of these adducts give dioxygenated sulfinate products. ,, …”