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Figure 1
Redox mechanism and Trx proteins in D. melanogaster. (a) Schematic description of the Trx–TrxR redox mechanism adapted from Collet & Messens (2010BB5). The redox cycle starts with a reduced form of Trx with the catalytic cysteine (Cys32) in the form of a thiolate [Supplementary Fig. S1(a)]. This state is stabilized by a hydrogen bond to the second cysteine of the motif (the Cys35 SH group). The thiolate is then able to form a transient intermolecular disulfide bond with the cysteine present in the oxidized substrate. The catalytic cycle ends when Cys35 in the enzyme attacks this intermolecular disulfide and forms a new intramolecular bond with Cys32, releasing the reduced substrate and the oxidized enzyme (Fomenko et al., 2008BB15). Trx recovers its initial state by the action of the Trx reductase (TrxR), which reduces Trx using NADPH/FAD as a source of reducing equivalents. (b) Trx-containing proteins in D. melanogaster. UniProt codes and domains are indicated. Abbreviations: CBP, calcium-binding protein; PDI, protein disulfide isomerase; SO, sulfhydryl oxidase. The ioelectric points for the different Trx domains are as follows: 6.5 for Q7KMR7, 5.0 for Q9VYV3 (three domains), 6.6 for Q9V438 (two domains), 4.9 for Q7JQR3 and 5.1 for X2JGP4 (two domains). A sequence alignment of these domains is shown in Supplementary Fig. S1(b). (c) Alignment of selected Dhd protein sequences. An extended version of this alignment is shown in Supplementary Fig. S1(d). The species are named with acronyms. RefSeq codes and species are given in Supplementary Table S1. The catalytic region is indicated with a yellow box and conserved positively and negatively charged residues are highlighted as blue and purple bars, respectively. Secondary-structure elements based on the D. melanogaster structure determined in this work are shown above the alignment. To facilitate comparison with other Trx structures, the β1 strand is indicated in gray. (d) Alignment of selected TrxT proteins. An extended version of this alignment is shown in Supplementary Fig. S1(e). Names and RefSeq codes are given in Supplementary Table S2. Colors are as in (c). (e) Sequence comparison of the TrxT C-terminal domain. The boxed region indicates the cysteine-containing motif predicted to adopt an extended conformation by JPred (Drozdetskiy et al., 2015BB7). The sequence that forms a disulfide bond with Cys93 and adopts an extended conformation in the crystals is indicated in pink.

IUCrJ
Volume 8| Part 2| March 2021| Pages 281-294
ISSN: 2052-2525
https://doi.org/10.1107/S2052252521000221