Application of alpha-methyl selenocysteine as a tool for the study of selenoproteins.

Selenocysteine (Sec) is the 21st proteogenic amino acid and it is now widely accepted that Sec is involved in redox biochemistry when incorporated in proteins. However, many of the chemical mechanisms for Sec bioactivity remain unknown. Herein, we describe a derivative of Sec, alpha-methyl Sec ((αMe)Sec), that is a useful chemical tool to study selenoenzyme mechanisms.

The Marine Neurotoxin Brevetoxin (PbTx-2) Inhibits and Mammalian Thioredoxin Reductases by Targeting Different Residues.

The brevetoxins, neurotoxins produced by , the Florida red tide dinoflagellate, effect fish and wildlife mortalities and adverse public health and economic impacts during recurrent blooms. Knowledge of the biochemical consequences of toxin production for could provide insights into an endogenous role of the toxins, yet this aspect has not been thoroughly explored. In addition to neurotoxicity, the most abundant of the brevetoxins, PbTx-2, inhibits mammalian thioredoxin reductase (TrxR).

Aggregation State of Synergistic Antimicrobial Peptides.

By integrating various simulation and experimental techniques, we discovered that antimicrobial peptides (AMPs) may achieve synergy at an optimal concentration and ratio, which can be caused by aggregation of the synergistic peptides. On multiple time and length scales, our studies obtain novel evidence of how peptide coaggregation in solution can affect the disruption of membranes by synergistic AMPs. Our findings provide crucial details about the complex molecular origins of AMP synergy, which will help guide the future development of synergistic AMPs as well as applications of anti-infective peptide cocktail therapies.

Can Selenoenzymes Resist Electrophilic Modification? Evidence from Thioredoxin Reductase and a Mutant Containing α-Methylselenocysteine.

Selenocysteine (Sec) is the 21st proteogenic amino acid in the genetic code. Incorporation of Sec into proteins is a complex and bioenergetically costly process that evokes the following question: "Why did nature choose selenium?" An answer that has emerged over the past decade is that Sec confers resistance to irreversible oxidative inactivation by reactive oxygen species. Here, we explore the question of whether this concept can be broadened to include resistance to reactive electrophilic species (RES) because oxygen and related compounds are merely a subset of RES.

2,2'-Dipyridyl diselenide: A chemoselective tool for cysteine deprotection and disulfide bond formation.

There are many examples of bioactive, disulfide-rich peptides and proteins whose biological activity relies on proper disulfide connectivity. Regioselective disulfide bond formation is a strategy for the synthesis of these bioactive peptides, but many of these methods suffer from a lack of orthogonality between pairs of protected cysteine (Cys) residues, efficiency, and high yields. Here, we show the utilization of 2,2'-dipyridyl diselenide (PySeSePy) as a chemical tool for the removal of Cys-protecting groups and regioselective formation of disulfide bonds in peptides.

Facile removal of 4-methoxybenzyl protecting group from selenocysteine.

Historically, methods to remove the 4-methoxybenzyl (Mob)-protecting group from selenocysteine (Sec) in peptides have used harsh and toxic reagents. The use of 2,2'-dithiobis-5-nitropyridine (DTNP) is an improvement over these methods; however, many wash steps are required to remove the by-product contaminant 5-nitro-2-thiopyridine. Even with many washes, excess DTNP adheres to the peptide.

Synthesis of alpha-methyl selenocysteine and its utilization as a glutathione peroxidase mimic.

Selenocysteine (Sec) is the 21st amino acid in the genetic code where this amino acid is primarily involved in redox reactions in enzymes because of its high reactivity toward oxygen and related reactive oxygen species. Sec has found wide utility in synthetic peptides, especially as a replacement for cysteine. One limitation of using Sec in synthetic peptides is that it can undergo β-syn elimination reactions after oxidation, rendering the peptide inactive due to loss of selenium.

Selenium Drives a Transcriptional Adaptive Program to Block Ferroptosis and Treat Stroke.

Ferroptosis, a non-apoptotic form of programmed cell death, is triggered by oxidative stress in cancer, heat stress in plants, and hemorrhagic stroke. A homeostatic transcriptional response to ferroptotic stimuli is unknown. We show that neurons respond to ferroptotic stimuli by induction of selenoproteins, including antioxidant glutathione peroxidase 4 (GPX4).

Reduction of cysteine-S-protecting groups by triisopropylsilane.

Triisopropylsilane (TIS), a hindered hydrosilane, has long been utilized as a cation scavenger for the removal of amino acid protecting groups during peptide synthesis. However, its ability to actively remove S-protecting groups by serving as a reductant has largely been mischaracterized by the peptide community. Here, we provide strong evidence that TIS can act as a reducing agent to facilitate the removal of acetamidomethyl (Acm), 4-methoxybenzyl (Mob), and tert-butyl (Bu ) protecting groups from cysteine (Cys) residues in the presence of trifluoroacetic acid (TFA) at 37 °C.

Removal of the 5-nitro-2-pyridine-sulfenyl protecting group from selenocysteine and cysteine by ascorbolysis.

We previously reported on a method for the facile removal of 4-methoxybenzyl and acetamidomethyl protecting groups from cysteine (Cys) and selenocysteine (Sec) using 2,2'-dithiobis-5-nitropyridine dissolved in trifluoroacetic acid, with or without thioanisole. The use of this reaction mixture removes the protecting group and replaces it with a 2-thio(5-nitropyridyl) (5-Npys) group. This results in either a mixed selenosulfide bond or disulfide bond (depending on the use of Sec or Cys), which can subsequently be reduced by thiolysis.