al anticancer and other biological activities (47). MarE’s catalytic cycle was proposed to hugely mimic the ones of IDO/TDO and PrnB, with the formation of a superoxo intermediate, followed by the homolytic cleavage in the O bond to yield a cpd II ike species and an epoxide intermediate (21). MarE shows 23.83 of sequence identity with a bacterial TDO from C. metallidurans (CmTDO) (SI Appendix, Table S1), containing most of the necessary residues conserved in wellknown TDO homologs (21). The characterization of MarE enriches the functional diversities on the superfamily by adding a monooxygenation catalytic activity (21). The proposal of MarE as part of the TDO superfamily casts the very first doubt in regards to the definition of a heme-dependent dioxygenase superfamily, as it reinforces PrnB for any monooxygenase type of function. On the other hand, a three-dimensional structure of MarE will not be accessible yet for unambiguously establishing its proteins superfamily assignment, although it is actually anticipated to have a similar fold with TDO and constitutes a separate new subgroup within the phylogenetic tree.actinobacteria, Streptomyces, have attracted attention on account of their oxygen-utilizing capability and sequence/structure homology towards the proteins on the TDO superfamily. These two enzymes usually do not react with tryptophan metabolites. As shown in Scheme two, SfmD is a 3-methyl–tyrosine hydroxylase within the biosynthetic pathway of saframycin A (48). SfmD can make use of ERĪ± custom synthesis hydrogen peroxide, or molecular dioxygen with ascorbate as a cosubstrate, to make 3-hydroxy-5-methyl–tyrosine (18). The crystal structure of SfmD has been characterized as a homolog of TDO superfamily containing a novel c-type heme cofactor using a single thioether covalent linkage in addition to a bis-histidine ligand set within the exceptional HxnHxxxC (n 38) heme-binding motif (18). The overall structure of SfmD resembles those other members of your superfamily (Fig. 2A). In distinct, the C terminus of SfmD aligns with CmTDO with an rmsd of two.26 for 102 C atoms (18). Although SfmD shares less than 20 of sequence identity using the founding members from the superfamily, the crystal structure establishes SfmD as a structural homolog in the superfamily. LmbB2 and Orf13 are heme-dependent TyrH found inside the biosynthetic pathway of lincomycin and anthramycin, promoting the formation of three,4-dihydroxy–phenylalanine (-DOPA) from -tyrosine (491). A homolog from a thermophilic bacterium Streptomyces sclerotialus (SsTyrH) has been functionally and structurally characterized not too long ago (19). SsTyrH shows structural homology together with the members from the TDO superfamily (Fig. 2B). The crystal structure of SsTyrH superposes SfmD (Fig. 2C). Despite the fact that SfmD and TyrH enzymes catalyze extremely equivalent hydroxylation reactions on tyrosine metabolites, the SsTyrH crystal structure reveals a b-type histidine-ligated heme, in Caspase 3 custom synthesis contrast for the c-type bis-histidyl igated heme in SfmD. It has also been noted that the heme position of SsTyrH aligns with these on the TDO superfamily members but differs from the heme position from the resting state structure of SfmD (Fig. 2D). Like MarE, SfmD and TyrH can make use of molecular oxygen as the oxidant in the presence of ascorbate, although the in vitro activities are around two orders of magnitude slower compared to the reaction with hydrogen peroxide: SfmD, kcat = 32.4 6 1.six min with H2O2, kcat = 0.029 6 0.001 mMmin with ascorbate and O2; Orf13 (TyrH), kobs = 34 six four min with H2O2, kobs = 0.58 6 0.01 min with