Selenoglutathione Diselenide: Unique Redox Reactions in the GPx-Like Catalytic Cycle and Repairing of Disulfide Bonds in Scrambled Protein

Abstract

Selenoglutathione (GSeH) is a selenium analogue of naturally abundant glutathione (GSH). In this study, this water-soluble small tripeptide was synthesized in a high yield (up to 98%) as an oxidized diselenide form, i.e., GSeSeG (1), by liquid-phase peptide synthesis (LPPS). Obtained 1 was applied to the investigation of the glutathione peroxidase (GPx)-like catalytic cycle. The important intermediates, i.e., GSe and GSeSG, besides GSeOH were characterized by Se NMR spectroscopy. Thiol exchange of GSeSG with various thiols, such as cysteine and dithiothreitol, was found to promote the conversion to GSe significantly. In addition, disproportionation of GSeSR to 1 and RSSR, which would be initiated by heterolytic cleavage of the Se-S bond and catalyzed by the generated selenolate, was observed. On the basis of these redox behaviors, it was proposed that the heterolytic cleavage of the Se-S bond can be facilitated by the interaction between the Se atom and an amino or aromatic group, which is present at the GPx active site. On the other hand, when a catalytic amount of 1 was reacted with scrambled 4S species of RNase A in the presence of NADPH and glutathione reductase, native protein was efficiently regenerated, suggesting a potential use of 1 to repair misfolded proteins through reduction of the non-native SS bonds.

Modeling Thioredoxin Reductase‐Like Activity with Cyclic Selenenyl Sulfides: Participation of an NH⋅⋅⋅Se Hydrogen Bond through Stabilization of the Mixed Se−S Intermediate

“…However, ab initio calculations for selenenyl sulfides 2a and 3a in water showed that, in the most stable conformation, there is no interaction between the SeÀS bond and the amino group, and the LUMO energy levels are almostc omparable with each other (see the SupportingI nformation). The other is the presence of an intramolecular NH···Se hydrogen bond for transienti ntermediate I',a ss hown in Figure 8a, which would suppress the reverse reaction to SeÀS ox and promote the nucleophilic attack of as econd thiol at the S atom to produce intermediate I.I waoka and co-workers previously proposed that as imilar NH···Se hydrogen bond in as elenenyl sulfide speciesc an accelerate cleavage of the SeÀSb ond duringt he GPx-like catalytic cycle of diselenide selenoglutathione( GSeSeG) [17] and dipeptide SecÀCys. [18] Ab initio calculation at HF/6-31 ++G(d,p) in water revealed that the most stable conformation has aN H···Se hydrogen bond for both selenenyls ulfides 12 and 13,a ss hown in Figure 8a.…”

Diselenolane‐Mediated Cellular Uptake: Efficient Cytosolic Delivery of Probes, Peptides, Proteins, Artificial Metalloenzymes and Protein‐Coated Quantum Dots

“…[26] A striking similarityw ith the repair of misfolded protein with diselenides furthers upports the walkerh ypothesis because this catalytic process hasb een studied in detail and shown to occur also in vivo. [16] However,i ndependent of the mode of action, the superb substrate scope identified in this study togetherw ith the small size, synthetic accessibility,s tability, solubility,l ow toxicity and high efficiency promise that diselenolane-mediated cellular uptake could become quite useful in practice. Particularly interesting is the efficient cytosolic delivery of two orders of magnitude larger substrates like protein-coated quantumd ots (diameter % 15 nm) by the miniscule diselenolanes (diameter % 0.3 nm), as tunning disproportion that is reminiscent of the ant carrying the elephant.…”

“…Using mostly topics that have been developed recently to characterize the large CPD polymers, [5,6] we here report that cellular uptake of the tiny diselenolanes is compatible with the cytosolic deliveryo fab road variety of functional substrates with diameters up to 15 nm. The combination of this broad substrate tolerance with insights from models tudies call for a mode of action that envisions DiSeL as molecular walkers [15] that move along disulfide tracks in transmembrane proteins, causing temporary local denaturation [16] and the appearance of adaptivem icellar membrane defects. [17] The biotinylated DiSeL tag 8 was synthesized [18] for general non-covalent connection to the substrate through the tetravalent streptavidin (Sav) 9,a% 60 kDa protein ( Figure 2).…”

“…[11] At entativem ode of action considers that rapid opening of the diselenolane with an exofacialthiol produces aselenolatethat remains deprotonated even under slightly acidic conditions ( Figure 5). Exchange of this reactive selenolate initiates amolecular walk [15] along disulfide tracks across the membrane, causing temporary protein denaturation [16] on one side and the temporary appearance of adaptive, non-leaky and self-healing micellar defects [17] on the other side, thus assuring compatibilityw ith the translocation of substrates of variable, even very large size ( Figure 5). Release into the cytosol is conceivable by favorable ring closure [11] or by exchange with glutathione.…”

The Opening of 1,2‐Dithiolanes and 1,2‐Diselenolanes: Regioselectivity, Rearrangements, and Consequences for Poly(disulfide)s, Cellular Uptake and Pyruvate Dehydrogenase Complexes

“…8), and selenophilicity produces a strong preference for diselenides over mixed selenosulfides. [29][30][31][32][33][34][35][36] As a result, 3-alkyl-1,2diselenolanes prefer to stay closed, and fast exchange makes it challenging to catch selenosulfides and demonstrate that 1,2-diselenolanes really do exchange with thiolates. [27] In the following, this question is clarified, also with regard to post-exchange rearrangements that may or may not account for the intriguing power of 3-alkyl-1,2-diselenolanes to enter into cells.…”