A crosslinker-based identification of redox relay targets.

Thiol-based redox control is among the most important mechanisms for maintaining cellular redox homeostasis, with essential participation of cysteine thiols of oxidoreductases. To explore cellular redox regulatory networks, direct interactions among active cysteine thiols of oxidoreductases and their targets must be clarified. We applied a recently described thiol-ene crosslinking-based strategy, named divinyl sulfone (DVSF) method, enabling identification of new potential redox relay partners of the cytosolic oxidoreductases thioredoxin (TXN) and thioredoxin domain containing 17 (TXNDC17). Applying multiple methods, including classical substrate-trapping techniques, will increase understanding of redox regulatory mechanisms in cells.

Functional profiling of asymmetrically-organized human CCT/TRiC chaperonin.

Molecular organization of the eukaryote chaperonin known as CCT/TRiC complex was recently clarified. Eight distinct subunits are uniquely organized, providing a favorable folding cavity for specific client proteins such as tubulin and actin. Because of its heterogeneous subunit composition, CCT complex has polarized inner faces, which may underlie an essential part of its chaperonin function. In this study, we structurally characterized the closed and open states of CCT complex, using molecular dynamics analyses. Our results showed that the inter-subunit interaction energies were asymmetrically distributed and were remodeled during conformational changes of CCT complex. In addition, exploration of redox related characteristics indicated changes in inner surface properties, including electrostatic potential, pKa and exposure of inner cysteine thiol groups, between the closed and open states. Cysteine activation events were experimentally verified by interaction analyses, using tubulin as a model substrate. Our data highlighted the importance of dynamics-based structural profiling of asymmetrically oriented chaperonin function.

Effect of light and auxin transport inhibitors on endoreduplication in hypocotyl and cotyledon.

KEY MESSAGE: Enhancement of endoreduplication in dark-grown hypocotyl is a common feature in dicotyledonous polysomatic plants, and TIBA-mediated inhibition of the endoreduplication is partially due to abnormal actin organization. Many higher plant species use endoreduplication during cell differentiation. However, the mechanisms underlying this process have remained elusive. In this study, we examined endoreduplication in hypocotyls and cotyledons in response to light in some dicotyledonous plant species. Enhancement of endoreduplication was found in the dark-grown hypocotyls of all the polysomatic species analyzed across five different families, indicating that this process is a common feature in dicotyledonous plants having polysomatic tissues. Conversely, endoreduplication was enhanced in the light-grown cotyledons in four of the five species analyzed. We also analyzed the effect of a polar auxin transport inhibitor, 2,3,5-triiodobenzoic acid (TIBA) on endoreduplication in hypocotyl and cotyledon tissues of radish (Raphanus sativus L. var. longipinnatus Bailey). TIBA was found to inhibit and promote endoreduplication in hypocotyls and cotyledons, respectively, suggesting that the endoreduplication mechanism differs in these organs. To gain insight into the effect of TIBA, radish and spinach (Spinacia oleracea L.) seedlings were treated with a vesicle-trafficking inhibitor, brefeldin A, and an actin polymerization inhibitor, cytochalasin D. Both of the inhibitors partially inhibited endoreduplication of the dark-grown hypocotyl tissues, suggesting that the prominent inhibition of endoreduplication by TIBA might be attributed to its multifaceted role.

Redox Sensitivities of Global Cellular Cysteine Residues under Reductive and Oxidative Stress.

The protein cysteine residue is one of the amino acids most susceptible to oxidative modifications, frequently caused by oxidative stress. Several applications have enabled cysteine-targeted proteomics analysis with simultaneous detection and quantitation. In this study, we employed a quantitative approach using a set of iodoacetyl-based cysteine reactive isobaric tags (iodoTMT) and evaluated the transient cellular oxidation ratio of free and reversibly modified cysteine thiols under DTT and hydrogen peroxide (H2O2) treatments. DTT treatment (1 mM for 5 min) reduced most cysteine thiols, irrespective of their cellular localizations. It also caused some unique oxidative shifts, including for peroxiredoxin 2 (PRDX2), uroporphyrinogen decarboxylase (UROD), and thioredoxin (TXN), proteins reportedly affected by cellular reactive oxygen species production. Modest H2O2 treatment (50 µM for 5 min) did not cause global oxidations but instead had apparently reductive effects. Moreover, with H2O2, significant oxidative shifts were observed only in redox active proteins, like PRDX2, peroxiredoxin 1 (PRDX1), TXN, and glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Overall, our quantitative data illustrated both H2O2- and reduction-mediated cellular responses, whereby while redox homeostasis is maintained, highly reactive thiols can potentiate the specific, rapid cellular signaling to counteract acute redox stress.