Thioredoxin reductase (TrxR) is an enzyme that belongs to a class of selenium-containing pyridine nucleotide-disulfide oxidoreductasesand is utilized by all known living organisms.[1] Although TrxR is primarily responsible for the reduction of thioredoxin, a small peptide,[2] its primary substrate specificity is relatively low making it a key drug target against several diseases such as cancer[3] and rheumatoid arthritis.[4] The active site dyad in mammalian TrxR contains vicinal cysteine (C)-selenocysteine (U) while in non-mammalian systems it consists of two vicinal cysteine residues. These dyads form a flexible eight-membered ring, which is not resolved in any available crystal structures.[5] This investigation is intended to understand the conformational equilibrium of these eight-membered rings using chemical computations. Monte Carlo simulations were performed to generate an initial set of conformations for the dyad ring (UU/CC/CU/UC dyads), followed by more accurate energetic evaluation using Density Functional Theory (DFT) methods. Obtained free energies of various local minima were utilized to acquire Boltzmann distributions of dyads at physiological temperature. Further, we calculated the NMR shifts of these conformers for future experiments. We will present the differences in conformational equilibrium of the aforesaid truncated dyads. These dyads will be utilized along with previously reported crystal structures of TrxR to prepare a full-scale enzyme model for subsequent studies. [1] Mustacich, D.; Powis, G. Biochem J. 2000, 346, 1-8. [2] Arnér, E. S. J.; Holmgren, A. Eur. J. Biochem. 2000, 267, 6102-6109. [3] Liu, Y.; Li, Y.; Yu, S.; Zhao, G. Curr. Drug Targets. 2012, 13, 1432-1444. [4] Maurice, M. M.; Nakamura, H.; Gringhuis, S.; Okamoto, T.; Yoshida, S.; Kullmann, F.; Lechner, S.; van der Voort, E. A.; Leow, A.; Versendaal, J.; Muller-Ladner, U.; Yodoi, J.; Tak, P. P.; Breedveld, F. C.; Verweij, C. L. Arthritis Rheum. 1999, 42, 2430-2439. [5] Gladyshev, V. N.; Jeang, K.-T.; Stadtman, T. C. Proc. Natl. Acad. Sci. USA 1996, 93, 6146-6151.

Conformational distribution of cysteine and selenocysteine dyads in biological redox processes

249th National Meeting (2015)

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