Sequence diversity and conservation in factors influencing succinate dehydrogenase flavinylation

Lycorine protects against septic myocardial injury by activating AMPK-related pathways

Cardiac dysfunction is a common complication in patients with sepsis triggering high morbidity and mortality. Lycorine (LYC), the main effective monomer component extracted from Lycoris bulbs, possesses antiviral, anti-inflammatory, analgesic, liver protection properties. In this study, the effect of LYC pre- and post-treatment as well as the underlying mechanism were evaluated in the cecal ligation and puncture (CLP) model of Balb/c mice. The survival rate, anal temperature, sepsis score, blood biochemical/routine indicators, cardiac function, sepsis-related pathophysiological processes, and AMPK signaling in septic mice were observed by echocardiography, histological staining, western blot, qPCR, and etc. LYC pretreatment attenuated myocardial injury in septic mice by improving survival rate, sepsis score, blood biochemical/routine indicators, cardiac function and structure, inhibiting inflammation and oxidative stress, improving mitochondrial function, modulating endoplasmic reticulum stress, and activating AMPK pathway. In particular, AMPK deficiency and AMPK inhibitor (Compound C) partially reversed the protective effects of LYC in septic mice. In addition, LYC posttreatment also has slight protective phenotypes on septic myocardial injury, but the effect is not as ideal as pretreatment. Taken together, these findings suggest that LYC may be a potential drug for the treatment of sepsis.

The assembly of succinate dehydrogenase: a key enzyme in bioenergetics

Succinate dehydrogenase (SDH) also known as complex II or succinate:quinone oxidoreductase is an enzyme involved in both oxidative phosphorylation and tricarboxylic acid cycle; the processes that generate energy. SDH is a multi-subunit enzyme which requires a series of proteins for its proper assembly at several steps. This enzyme has medical significance as there is a broad range of human diseases from cancers to neurodegeneration related to SDH malfunction. Some of these disorders have recently been linked to defective assembly factors, reinvigorating further research in this area. Apart from that this enzyme has agricultural importance as many fungicides have been/will be designed targeting specifically this enzyme in plant fungal pathogens. In addition, we speculate it might be possible to design novel fungicides specifically targeting fungal assembly factors. Considering the medical and agricultural implications of SDH, the aim of this review is an overview of the SDH assembly factors and critical analysis of controversial issues around them.

Mitochondrial complex II of plants: subunit composition, assembly, and function in respiration and signaling

Complex II [succinate dehydrogenase (succinate-ubiquinone oxidoreductase); EC 1.3.5.1; SDH] is the only enzyme shared by both the electron transport chain and the tricarboxylic acid (TCA) cycle in mitochondria. Complex II in plants is considered unusual because of its accessory subunits (SDH5-SDH8), in addition to the catalytic subunits of SDH found in all eukaryotes (SDH1-SDH4). Here, we review compositional and phylogenetic analysis and biochemical dissection studies to both clarify the presence and propose a role for these subunits. We also consider the wider functional and phylogenetic evidence for SDH assembly factors and the reports from plants on the control of SDH1 flavination and SDH1-SDH2 interaction. Plant complex II has been shown to influence stomatal opening, the plant defense response and reactive oxygen species-dependent stress responses. Signaling molecules such as salicyclic acid (SA) and nitric oxide (NO) are also reported to interact with the ubiquinone (UQ) binding site of SDH, influencing signaling transduction in plants. Future directions for SDH research in plants and the specific roles of its different subunits and assembly factors are suggested, including the potential for reverse electron transport to explain the succinate-dependent production of reactive oxygen species in plants and new avenues to explore the evolution of plant mitochondrial complex II and its utility.

Proteomic and Carbonylation Profile Analysis at the Critical Node of Seed Ageing in Oryza sativa

The critical node (CN), which is the transition from the plateau phase to the rapid decreasing phase of seed ageing, is extremely important for seed conservation. Although numerous studies have investigated the oxidative stress during seed ageing, information on the changes in protein abundance at the CN is limited. In this study, we aimed to investigate the abundance and carbonylation patterns of proteins at the CN of seed ageing in rice. The results showed that the germination rate of seeds decreased by less than 20% at the CN; however, the abundance of 112 proteins and the carbonylation levels of 68 proteins markedly changed, indicating oxidative damage. The abundance and activity of mitochondrial, glycolytic, and pentose phosphate pathway proteins were reduced; consequently, this negatively affected energy production and germination. Proteins related to defense, including antioxidant system and heat shock proteins, also reduced in abundance. Overall, energy metabolism was reduced at the CN, leading to a decrease in the antioxidant capacity, whereas seed storage proteins were up-regulated and carbonylated, indicating that the seed had a lower ability to utilize seed storage proteins for germination. Thus, the significant decrease in metabolic activities at the CN might accelerate the loss of seed viability.

Expression of genes encoding subunits A and B of succinate dehydrogenase in germinating maize seeds is regulated by methylation of their promoters

Succinate dehydrogenase (SDH) activity, isoenzyme pattern, and expression of two genes encoding subunit A and of three genes encoding subunit B have been investigated in the scutellum of germinating maize (Zea mays L.) seeds. Four SDH isoforms were detected electrophoretically and by ion-exchange chromatography at the peak of activity of the glyoxylate cycle (on the 4th and 5th day of germination), while in dry seeds and on the 8th and 9th day of germination only two isoforms were present, which can be related to differential expression of the genes encoding SDH subunits. The levels of transcription of Sdh1-1, Sdh1-2, Sdh2-1, Sdh2-2 and Sdh2-3 and the intensity of methylation of their promoters have been determined. In the course of seed germination, the level of methylation of the promoters of one gene encoding subunit A (Sdh1-1) and of two genes encoding subunit B (Sdh2-1 and Sdh2-2) changed from low to the highest, which resulted in suppression of their transcription during the period when the intensity of the glyoxylate cycle was decreasing, while methylation of the promoter of Sdh2-3 did not change and expression of this gene was constitutive during germination. Methylation of the promoter of Sdh1-2 increased but less sharply as compared to Sdh1-1. It is suggested that epigenetic mechanisms of SDH expression via methylation of promoters play an important role in the regulation of transcription of Sdh1-1, Sdh2-1 and Sdh2-2 in maize seeds during germination. These genes may play a role in the provision of operation of the glyoxylate cycle, while Sdh1-2 and Sdh2-3 are involved mainly in the respiratory processes that are not connected with utilization of succinate formed in the glyoxylate cycle.

Cassava root membrane proteome reveals activities during storage root maturation

Cassava (Manihot esculenta Crantz) is one of the most important crops of Thailand. Its storage roots are used as food, feed, starch production, and be the important source for biofuel and biodegradable plastic production. Despite the importance of cassava storage roots, little is known about the mechanisms involved in their formation. This present study has focused on comparison of the expression profiles of cassava root proteome at various developmental stages using two-dimensional gel electrophoresis and LC-MS/MS. Based on an anatomical study using Toluidine Blue, the secondary growth was confirmed to be essential during the development of cassava storage root. To investigate biochemical processes occurring during storage root maturation, soluble and membrane proteins were isolated from storage roots harvested from 3-, 6-, 9-, and 12-month-old cassava plants. The proteins with differential expression pattern were analysed and identified to be associated with 8 functional groups: protein folding and degradation, energy, metabolism, secondary metabolism, stress response, transport facilitation, cytoskeleton, and unclassified function. The expression profiling of membrane proteins revealed the proteins involved in protein folding and degradation, energy, and cell structure were highly expressed during early stages of development. Integration of these data along with the information available in genome and transcriptome databases is critical to expand knowledge obtained solely from the field of proteomics. Possible role of identified proteins were discussed in relation with the activities during storage root maturation in cassava.

The conserved RGxxE motif of the bacterial FAD assembly factor SdhE is required for succinate dehydrogenase flavinylation and activity

Succinate dehydrogenase (SDH) is an important respiratory enzyme that plays a critical role in the generation of energy in the majority of eukaryotes, bacteria, and archaea. The activity of SDH is dependent on the covalent attachment of the redox cofactor FAD to the flavoprotein subunit SdhA. In the Gram-negative bacteria Escherichia coli and Serratia sp. ATCC 39006, the covalent attachment of FAD to SdhA is dependent on the FAD assembly factor SdhE (YgfY). Although mechanisms have been proposed, experimental evidence that elucidates the molecular details of SdhE-mediated flavinylation are scarce. In this study, truncation and alanine swap mutagenesis of SdhE identified a highly conserved RGxxE motif that was important for SdhE function. Interestingly, RGxxE site-directed variants were not impaired in terms of protein folding or interactions with SdhA. Purification and analysis of SdhA from different mutant backgrounds demonstrated that SdhE interacts with and flavinylates folded SdhA without a requirement for the assembly of the entire SDH complex. SdhA was also partially active in the absence of SdhE, suggesting that SdhA is able to attach FAD through an inefficient autocatalytic mechanism. The results presented are of widespread relevance because SdhE and SDH are required for bacterial pathogenesis and mutations in the eukaryotic homologues of SdhE and SDH are associated with cancer in humans.