# Structural and Biochemical Characterization of Thioredoxin-2 from _Deinococcus radiotrans_
## 4 Conclusions  
Since the first three-dimensional structure of Trx in _E. coli_ was reported, many Trx structures, in a wide range of species, have been reported. Structural analyses of Trx proteins have revealed the detailed mechanism underlying thiol/disulfide exchange, as well as the conserved amino acids responsible for maintaining the active site in its functional state, and even the evolutionary diversity that exists in this ubiquitous protein family. Although the number of identified Trx2 in bacteria is growing continuously and despite Trx2 being known to conduct important roles in the regulation of the cellular redox state and oxidative stress response in bacteria, information regarding the structure and function of bacterial Trx2 has been much less than that for Trx1, until now. Here, we present atomic level details of the structure of full-length DrTrx2. The most significant difference between it and the other two reported full-length Trx2 structures is the orientation of the N-terminal zinc-finger domain, which is known to be involved in protein-protein interactions. The reduction activity of DrTrx2 was decreased by defective zinc binding, but not fully eliminated. Unlike in _E. coli_, the expression levels of _drtrx1_ and _drtrx2_ were increased and the deletion of these genes produced a sensitive phenotype under exposure to H\({}_{2}\)O\({}_{2}\). Considered together, our recent structural and functional characterizations of Trx proteins from multi-stress resistant _D. radiotrans_ may enhance our knowledge regarding the cellular function of bacterial Trx2 proteins.  
**Supplementary Materials:** The following are available online at [[https://www.mdpi.com/article/10.3390/antiox10111843/s1](https://www.mdpi.com/article/10.3390/antiox10111843/s1)]([https://www.mdpi.com/article/10.3390/antiox10111843/s1](https://www.mdpi.com/article/10.3390/antiox10111843/s1)), Figure S1: Complementation of _Adtrtrx1_ and _Adtrtrx2_, Figure S2: Transcription of _dtrtrx1_ and _dtrtrx2_ in _AdracyR_ mutant under H\({}_{2}\)O\({}_{2}\) stress, Figure S3: The structure-based sequence alignment of DrTrx2 with DrTrx1, Figure S4: Reduction of insulin and DTNB by cysteine mutant Trx proteins, Figure S5: Structural comparison of DrTrx2, RcTrx2, and YbTrx2, Figure S6: Interdomain interactions, Table S1: Bacterial strains and plasmids used in this study, Table S2. Primers used for gene cloning, Table S3. Zinc concentrations measured by ICP-OES.  
**Author Contributions:** Conceptualization, M.-K.K. and S.L.; methodology, L.Z., S.J., J.Z., J.-H.J. and H.S.S.; software, M.-K.K. and L.Z.; validation, M.-K.K. and S.L.; formal analysis, L.Z. and J.-i.C.; investigation, M.-K.K. and L.Z.; resources, M.-K.K. and L.Z.; data curation, M.-K.K. and L.Z.; writing--original draft preparation, M.-K.K. and L.Z.; writing--review and editing, M.-K.K. and L.Z.; visualization, M.-K.K. and L.Z.; supervision, M.-K.K. and S.L.; project administration, M.-K.K. and S.L.; funding acquisition, M.-K.K. and S.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This study was supported by the Nuclear R&D program of Ministry of Science and ICT (MSIT), Republic of Korea, and the National Research Foundation of Korea (NRF-2020R1F1A1057780 to M.-K.K., L.Z. and J.Z.) Grant.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The atomic coordinates and structure factors for DrTrx2 have been deposited in the Protein Data Bank, with the accession code 7D6L. Other data is contained within this article and Supplementary File.  
**Acknowledgments:** We thank the beamline staff at Pohang Light Source for supporting data collection.  
**Conflicts of Interest:** The authors declare no conflict of interest.