Recent development of polysulfides: Chemistry and biological applications

Polysulfides (RSS_nSR, n ≥ 1) are a class of sulfane sulfur compounds that have gained significant recent attention due to their connections to hydrogen sulfide (H₂S) and hydropersulfides (RSSH), which are known to play important roles in redox signaling. While the potential regulatory functions of polysulfides in biological systems have been recognized for a long time, understanding their interactions with H₂S/RSSH have only recently begun. In this Mini Review, some of the most recent discoveries of polysulfides within biological contexts are summarized and these include their biological formation pathways, detection methods for animal and plant samples, properties, and unique functions. These studies have set up a solid foundation for understanding polysulfide biology, and more mechanistic details are expected to be discovered in the coming years.     

Diacyl disulfides as the precursors for hydrogen persulfide (H2S2)

While hydrogen polysulfides (H₂S_n, n ≥ 2) are believed to play regulatory roles in biology, their fundamental chemistry and reactivity are still poorly understood. Compounds that can produce H₂S_n are useful tools. In this work we found that H₂S₂ could be effectively produced from diacyl disulfide precursors, triggered by certain nucleophiles, in both aqueous solutions and organic solvents. This method was used to explore redox reactions of H₂S₂, such as scavenging 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and reduction of tetrazines.     

Sunlight-driven rapid and facile synthesis of Silver nanoparticles using Allium ampeloprasum extract with enhanced antioxidant and antifungal activity

Green nanotechnology has acquired immense demand due to its cost-effective, eco-friendly and benevolent approach for the synthesis of nanoparticles. Among the biological methods, plants aid as a significant green resource for synthesizing nanoparticles that are safe and non-toxic for human use. In the present investigation, Silver nanoparticles (AgNPs) were synthesized using bulbs extract of Allium ampeloprasum under the influence of sunlight irradiation and characterized using different techniques. Distinct in-vitro assays were performed to test the antioxidant and anticandida potential of the synthesized AgNPs. Results suggested the efficient and rapid sunlight-driven synthesis of AgNPs using A. ampeloprasum extract. UV–Vis spectrum showed absorption peak at 446 nm which confirmed the formation of AgNPs. FTIR analysis suggested the presence of functional groups associated with flavonoids and sulfur compounds in A. ampeloprasum extract. The synthesized AgNPs showed Face Centred Cubic (FCC) structure with an average size of 35 nm. Spherical, quasi spherical, triangular and ellipsoidal morphology of the NPs were observed from the TEM micrograph. The synthesized AgNPs showed pronounced free radical scavenging potential for DPPH, ABTS?+ and H₂O₂ radicals. The anticandida potency of the synthesized AgNPs was observed as follows: C. albicans ≥ C. tropicalis ≥ C. glabrata ≥ C. parapsilosis ≥ C. krusei. Results showed that sunlight driven nanoparticle synthesis of AgNPs is rapid, facile and exhibit enhanced antioxidant and antifungal activity.     

The multifaceted roles of sulfane sulfur species in cancer-associated processes

Sulfane sulfur species comprise a variety of biologically relevant hydrogen sulfide (H₂S)-derived species, including per- and poly-sulfidated low molecular weight compounds and proteins. A growing body of evidence suggests that H₂S, currently recognized as a key signaling molecule in human physiology and pathophysiology, plays an important role in cancer biology by modulating cell bioenergetics and contributing to metabolic reprogramming. This is accomplished through functional modulation of target proteins via H₂S binding to heme iron centers or H₂S-mediated reversible per- or poly-sulfidation of specific cysteine residues. Since sulfane sulfur species are increasingly viewed not only as a major source of H₂S but also as key mediators of some of the biological effects commonly attributed to H₂S, the multifaceted role of these species in cancer biology is reviewed here with reference to H₂S, focusing on their metabolism, signaling function, impact on cell bioenergetics and anti-tumoral properties.     

Redox chemistry and chemical biology of H2S,hydropersulfides, and derived species: Implications of their possible biological activity and utility

Hydrogen sulfide (H₂S) is an endogenously generated and putative signaling/effector molecule. Despite its numerous reported functions, the chemistry by which it elicits its functions is not understood. Moreover, recent studies allude to the existence of other sulfur species besides H₂S that may play critical physiological roles. Herein, the basic chemical biology of H₂S as well as other related or derived species is discussed and reviewed. This review particularly focuses on the per- and polysulfides which are likely in equilibrium with free H₂S and which may be important biological effectors themselves.     

The interaction between H<Subscript>2</Subscript>O<Subscript>2</Subscript> and NO,Ca<Superscript>2+</Superscript>, cGMP,and MAPKs during adventitious rooting in mung bean seedlings

Hydrogen peroxide (H₂O₂), an active oxygen species, is widely generated in many biological systems and mediates various physiological and biochemical processes in plants. In the present study, we present a signaling network involving H₂O₂, nitric oxide (NO), calcium (Ca²⁺), cyclic guanosine monophosphate (cGMP), and the mitogen-activated protein kinase (MAPK) cascade during adventitious rooting in mung bean seedlings. Both exogenous H₂O₂ and the NO donor sodium nitroprussiate were capable of promoting the formation and development of adventitious roots. H₂O₂ and NO signaling pathways were elicited in parallel in auxin-induced adventitious rooting. Cytosolic Ca²⁺ was required for adventitious rooting, and Ca²⁺ served as a downstream component of H₂O₂, as well as cGMP or MAPK, signaling cascades. cGMP and MAPK cascades function downstream of H₂O₂ signaling and depend on auxin responses in adventitious root signaling processes.     

Hydrogen sulfide interacts with calcium signaling to enhance the chromium tolerance in Setaria italica

The oscillation of intracellular calcium (Ca²⁺) concentration is a primary event in numerous biological processes in plants, including stress response. Hydrogen sulfide (H₂S), an emerging gasotransmitter, was found to have positive effects in plants responding to chromium (Cr⁶⁺) stress through interacting with Ca²⁺ signaling. While Ca²⁺ resemblances H₂S in mediating biotic and abiotic stresses, crosstalk between the two pathways remains unclear. In this study, Ca²⁺ signaling interacted with H₂S to produce a complex physiological response, which enhanced the Cr⁶⁺ tolerance in foxtail millet (Setaria italica). Results indicate that Cr⁶⁺ stress activated endogenous H₂S synthesis as well as Ca²⁺ signaling. Moreover, toxic symptoms caused by Cr⁶⁺ stress were strongly moderated by 50 μM H₂S and 20 mM Ca²⁺. Conversely, treatments with H₂S synthesis inhibitor and Ca²⁺ chelators prior to Cr⁶⁺-exposure aggravated these toxic symptoms. Interestingly, Ca²⁺ upregulated expression of two important factors in metal metabolism, MT3A and PCS, which participated in the biosynthesis of heavy metal chelators, in a H₂S-dependent manner to cope with Cr⁶⁺ stress. These findings also suggest that the H₂S dependent pathway is a component of the Ca²⁺ activating antioxidant system and H₂S partially contributes Ca²⁺-activating antioxidant system.     

Autotrophic and Mixotrophic Hydrogen Photoproduction in Sulfur-Deprived Chlamydomonas Cells

In Chlamydomonas reinhardtii cells, H₂ photoproduction can be induced in conditions of sulfur deprivation in the presence of acetate. The decrease in photosystem II (PSII) activity induced by sulfur deprivation leads to anoxia, respiration becoming higher than photosynthesis, thereby allowing H₂ production. Two different electron transfer pathways, one PSII dependent and the other PSII independent, have been proposed to account for H₂ photoproduction. In this study, we investigated the contribution of both pathways as well as the acetate requirement for H₂ production in conditions of sulfur deficiency. By using 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), a PSII inhibitor, which was added at different times after the beginning of sulfur deprivation, we show that PSII-independent H₂ photoproduction depends on previously accumulated starch resulting from previous photosynthetic activity. Starch accumulation was observed in response to sulfur deprivation in mixotrophic conditions (presence of acetate) but also in photoautotrophic conditions. However, no H₂ production was measured in photoautotrophy if PSII was not inhibited by DCMU, due to the fact that anoxia was not reached. When DCMU was added at optimal starch accumulation, significant H₂ production was measured. H₂ production was enhanced in autotrophic conditions by removing O₂ using N₂ bubbling, thereby showing that substantial H₂ production can be achieved in the absence of acetate by using the PSII-independent pathway. Based on these data, we discuss the possibilities of designing autotrophic protocols for algal H₂ photoproduction.     

RXR agonists inhibit oxidative stress-induced apoptosis in H9c2 rat ventricular cells

Retinoid X receptor (RXR) plays a central role in the regulation of intracellular receptor signaling pathways. We examined its role in regulating oxidative stress-induced apoptosis in H9c2 rat ventricular cells. We showed for the first time that functional RXR protein was downregulated by hydrogen peroxide (H₂O₂) in H9c2 cardiomyocytes. Natural and synthetic agonists of RXR, 9-cis-RA, and LGD1069 respectively, prevented H₂O₂-triggered apoptosis, and this anti-apoptotic effect was inhibited by the RXR antagonist HX531. Further investigation into the protective mechanisms of RXR demonstrated that H₂O₂-induced loss of mitochondrial membrane potential, mitochondrial release of cytochrome c and caspase-3 activation were all significantly attenuated by pretreatment with RXR agonists. Furthermore, this protection was associated with a reduction in intracellular reactive oxygen species and an upregulation in catalase activity. Thus, these data indicate that pharmacological activation of RXR exerts protective effects against H₂O₂-induced apoptosis in H9c2 rat ventricular cells through antioxidant and mitochondria-protective mechanisms.     

The salt stress-induced LPA response in Chlamydomonas is produced via PLA₂ hydrolysis of DGK-generated phosphatidic acid

The unicellular green alga Chlamydomonas has frequently been used as a eukaryotic model system to study intracellular phospholipid signaling pathways in response to environmental stresses. Earlier, we found that hypersalinity induced a rapid increase in the putative lipid second messenger, phosphatidic acid (PA), which was suggested to be generated via activation of a phospholipase D (PLD) pathway and the combined action of a phospholipase C/diacylglycerol kinase (PLC/DGK) pathway. Lysophosphatidic acid (LPA) was also increased and was suggested to reflect a phospholipase A₂ (PLA₂) activity based on pharmacological evidence. The question of PA''s and LPA''s origin is, however, more complicated, especially as both function as precursors in the biosynthesis of phospho- and galactolipids. To address this complexity, a combination of fatty acid-molecular species analysis and in vivo ³²P-radiolabeling was performed. Evidence is provided that LPA is formed from a distinct pool of PA characterized by a high α-linolenic acid (18:3n-3) content. This molecular species was highly enriched in the polyphosphoinositide fraction, which is the substrate for PLC to form diacylglycerol. Together with differential ³²P-radiolabeling studies and earlier PLD-transphosphatidylation and PLA₂-inhibitor assays, the data were consistent with the hypothesis that the salt-induced LPA response is primarily generated through PLA₂-mediated hydrolysis of DGK-generated PA and that PLD or de novo synthesis [via endoplasmic reticulum - or plastid-localized routes] is not a major contributor.     

Identification of dimedone-trapped sulfenylated proteins in plants under stress

In stressed plants, the reactive oxygen species (ROS) levels rise. Key to ROS signaling research are detection and identification of the protein cysteine sulfenylation (-SOH), the ROS-mediated oxidative product of a thiol (-SH). Arabidopsis thaliana seedlings were stressed with hydrogen peroxide (H₂O₂) and the sulfenylated proteins were tagged with dimedone. Dimedone-tagged sulfenic acid proteins were visualized on a two-dimensional electrophoresis (2DE) immunoblot with an anticysteine sulfenic acid antibody and were subsequently detected by mass spectrometry. We optimized the detection method for protein sulfenylation in Arabidopsis. We conclude that dimedone can penetrate the cell wall, does not stress plants, and can “read” the changes in the protein sulfenylation pattern under oxidative stress. We observed that the number of sulfenylated proteins in plants treated with 10 mM H₂O₂ was higher than that in untreated plants. A total of 39 sulfenylated protein spots were found on 2DE immunoblots. By means of mass spectrometry, 11 sulfenylated proteins were discovered involved in primary metabolism, redox regulation, translation and signaling pathways. Hence, by combining an immunochemical 2DE strategy with mass spectrometry, we were able to identify sulfenylated proteins in H₂O₂-stressed Arabidopsis seedlings. The sulfenylated proteins can be considered for further validation as redox regulators in plants.     

Genetic diversity in Mentha cervina based on morphological traits,essential oils profile and ISSRs markers

Morphological, phytochemical and genetic differences were studied to evaluate the level and distribution of diversity in twelve populations of the Portuguese endangered medicinal plant Mentha cervina L. Morphological variation was correlated with ecological conditions at the site of origin. Pulegone was the major essential oils compound in all of the populations collected at full flowering (68–83%), in different growing conditions (51–82%), and for all the developmental stages studied (47–82%). Although clusters were defined, the analysis revealed a high chemical correlation among all populations (S_corr ≥ 0.95%). Inter-simple sequence repeats markers were used to assess the population structure and genetic variation. Populations exhibited a relatively low genetic diversity (PPB = 14.3–64.6%, H_e = 0.051–0.222, I = 0.076–0.332), with high structuring between them (G_ST = 0.51). However, the genetic diversity at species level was relatively high (PPB = 97.7%; H_e = 0.320). The levels and patterns of genetic diversity were assumed to result largely from a combination of evolutionary history and its unique biological traits, such as breeding system, clonal growth, low capacity of dispersion and habitat fragmentation. The relatively low genetic diversity in the populations analyzed indicates that the maintenance of their evolutionary potential is at risk if population sizes are maintained and if there is no protection of the habitats.     

Bounds on the total population for species governed by reaction-diffusion equations in arbitrary two-dimensional regions

Analysis based on the integration of differential inequalities is employed to derive upper and lower bounds on the total populationN(t) = ∫ _R θ(x ₁,x ₂,t) dx ₁ dx ₂ of a biological species with an area-density distribution function θ=θ(x ₁,x ₂,t) (≥0) governed by a reaction-diffusion equation of the form ∂θ/∂t =D∇²θ +fθ −gθ ⁿ⁺¹ whereD (>0),n (>0),f andg are constant parameters, θ=0 at all points on the boundary ∂R of an (arbitrary) two-dimensional regionR, and the initial distribution (θ(_{x 1},x ₂, 0) is such thatN(0) is finite. Forg≥0 withR the entire two-dimensional Euclidean space, a lower bound onN(t) is obtained, showing in particular thatN(∞) is bounded below by a finite positive quantity forf≥0 andn>1. An upper bound onN(t) is obtained for arbitrary bounded or unbounded)R withn=1,f andg negative, and ∫ _R θ(x ₁,x ₂, 0)² dx ₁ dx ₂ sufficiently small in magnitude, implying that the population goes to extinction with increasing values of the time,N(∞)=0. Forg≥0 andR of finite area, the analysis yields upper bounds onN(t), predicting eventual extinction of the population if eitherf≤0 or if the area ofR is less than a certain grouping of the parameters in cases for whichf is positive. These results are directly applicable to biological species with distributions satisfying the Fisher equation in two spatial dimensions and to species governed by certain specialized population models.     

Influence of the sulfur species reactivity on biofilm conformation during pyrite colonization by Acidithiobacillus thiooxidans

Massive pyrite (FeS₂) electrodes were potentiostatically modified by means of variable oxidation pulse to induce formation of diverse surface sulfur species (S _n ^2?, S⁰). The evolution of reactivity of the resulting surfaces considers transition from passive (e.g., Fe_1?x S₂) to active sulfur species (e.g., Fe_1?x S_2?y , S⁰). Selected modified pyrite surfaces were incubated with cells of sulfur-oxidizing Acidithiobacillus thiooxidans for 24 h in a specific culture medium (pH 2). Abiotic control experiments were also performed to compare chemical and biological oxidation. After incubation, the attached cells density and their exopolysaccharides were analyzed by confocal laser scanning microscopy (CLMS) and atomic force microscopy (AFM) on bio-oxidized surfaces; additionally, S _n ^2?/S⁰ speciation was carried out on bio-oxidized and abiotic pyrite surfaces using Raman spectroscopy. Our results indicate an important correlation between the evolution of S _n ^2?/S⁰ surface species ratio and biofilm formation. Hence, pyrite surfaces with mainly passive-sulfur species were less colonized by A. thiooxidans as compared to surfaces with active sulfur species. These results provide knowledge that may contribute to establishing interfacial conditions that enhance or delay metal sulfide (MS) dissolution, as a function of the biofilm formed by sulfur-oxidizing bacteria.     

The chemical biology of hydrogen sulfide and related hydropersulfides: interactions with biologically relevant metals and metalloproteins

Hydrogen sulfide and related/derived persulfides (RS_nH, RSS_nR, n > 1) have been the subject of recent research interest because of their reported physiological signaling roles. In spite of their described actions, the chemical/biochemical mechanisms of activity have not been established. From a chemical perspective, it is likely that metals and metalloproteins are possible biological targets for the actions of these species. Thus, the chemical biology of hydrogen sulfide and persulfides with metals and metalloproteins will be discussed as a prelude to future speculation regarding their physiological function and utility.     

The HydS C-terminal domain of the Thiocapsa bogorovii HydSL hydrogenase is involved in membrane anchoring and electron transfer

Thiocapsa bogorovii BBS (former name Thiocapsa roseopersicina) contains HydSL hydrogenase belonging to 1e subgroup of NiFe hydrogenases (isp-type). The operon of these hydrogenases contains gene for small subunit (hydS), gene for large subunit (hupL), and genes isp1 and isp2 between them. It is predicted that last two genes code electron transport careers for electron transfer from/to HydSL hydrogenase. However, the interaction between them is unclear. The aim of this study was to determine structural and functional role of T. bogorovii HydS C-terminal end. For this purpose, we modelled all subunits of the complex HydS-HydL-Isp1-Isp2. Hydrophobicity surface analysis of the Isp1 model revealed highly hydrophobic helices suggesting potential membrane localization, as well as the hydrophilic C-terminus, which is likely localized outside of membrane. Isp1 model was docked with models of full length and C-terminal truncated HydSL hydrogenases and results illustrate the possibility of HydSL membrane anchoring via transmembrane Isp1 with essential participation of C-terminal end of HydS in the interaction. C-terminal end of HydS subunit was deleted and our studies revealed that the truncated HydSL hydrogenase detached from cellular membranes in contrast to native hydrogenase. It is known that HydSL hydrogenase in T. bogorovii performs the reaction of elemental sulfur reduction (S₀ + H₂ = ≥H₂S). Cells with truncated HydS produced much less H₂S in the presence of H₂ and S₀. Thus, our data support the conclusion that C-terminal end of HydS subunit participates in interaction of HydSL hydrogenase with Isp1 protein for membrane anchoring and electron transfer.     

Oxygen and reactive oxygen species-dependent regulation of plant growth and development

Oxygen and reactive oxygen species (ROS) have been co-opted during evolution into the regulation of plant growth, development, and differentiation. ROS and oxidative signals arising from metabolism or phytohormone-mediated processes control almost every aspect of plant development from seed and bud dormancy, liberation of meristematic cells from the quiescent state, root and shoot growth, and architecture, to flowering and seed production. Moreover, the phytochrome and phytohormone-dependent transmissions of ROS waves are central to the systemic whole plant signaling pathways that integrate root and shoot growth. The sensing of oxygen availability through the PROTEOLYSIS 6 (PRT6) N-degron pathway functions alongside ROS production and signaling but how these pathways interact in developing organs remains poorly understood. Considerable progress has been made in our understanding of the nature of hydrogen peroxide sensors and the role of thiol-dependent signaling networks in the transmission of ROS signals. Reduction/oxidation (redox) changes in the glutathione (GSH) pool, glutaredoxins (GRXs), and thioredoxins (TRXs) are important in the control of growth mediated by phytohormone pathways. Although, it is clear that the redox states of proteins involved in plant growth and development are controlled by the NAD(P)H thioredoxin reductase (NTR)/TRX and reduced GSH/GRX systems of the cytosol, chloroplasts, mitochondria, and nucleus, we have only scratched the surface of this multilayered control and how redox-regulated processes interact with other cell signaling systems.

Oxygen and reactive oxygen species regulate plant growth, development, and differentiation through multiple interlinked signaling pathways.

Advances

• Developmentally regulated hypoxia and reactive oxygen species (ROS) production are key features of the stem cell niches, providing information about stem cell position, the environment, and metabolic state.
• Protein cysteine oxidation is central to oxygen and ROS signaling. However, S-nitrosylation, S-glutathionylation, S-sulfhydration, and S-sulfenylation modifications can occur on the same cysteine. The influence of each modification on stability, localization, and function remains unknown.
• Numerous intersecting ROS signaling pathways are probable and likely depend on the site of ROS production and the nature of the oxidized receptor protein. ROS sensors such as the hydrogen peroxide (H₂O₂)-INDUCED Ca²⁺ INCREASES 1 (HPCA1) leucine rich receptor kinase translate redox signals into protein modifications to regulate signaling cascades. H₂O₂ perception/transduction is dependent on thiol-dependent mechanisms policed by the ferredoxin/thioredoxin (TRX), NAD(P)H TRX reductase C (NTRC), reduced glutathione (GSH), and glutaredoxin (GRX) systems.
• ROS waves transmit redox signals from cell to cell in the apoplast, and probably through plasmodesmata. Long-distance transport of H₂O₂ and other ROS, therefore, appears to be unnecessary. Similarly, contact sites between organelles allow ROS transfer.
• Convergence points for oxygen and ROS signaling occur on proteins such as ROH OF PLANT 2 (ROP2) GTPase,RESPIRATORY BURST OXIDASE HOMOLOG D (RBOHD), and TRX-h to regulate meristematic activity via TARGET OF RAPAMYCIN (TOR) kinase activity.