Peroxiredoxin-5 (PRDX5), mitochondrial is a protein that in humans is encoded by the PRDX5 gene, located on chromosome 11. [5]
This gene encodes a member of the six-member peroxiredoxin family of antioxidant enzymes. Like the other five members, PRDX5 is widely expressed in tissues but differs by its large subcellular distribution. [6] In human cells, it has been shown that PRDX5 can be localized to mitochondria, peroxisomes, the cytosol, and the nucleus. [7] Human PRDX5 is identified by virtue of the sequence homologies to yeast peroxisomal antioxidant enzyme PMP20. [6] [8]
Biochemically, PRDX5 is a peroxidase that can use cytosolic or mitochondrial thioredoxins to reduce alkyl hydroperoxides or peroxynitrite with high rate constants in the 106 to 107 M−1s−1 range, whereas its reaction with hydrogen peroxide is more modest, in the 105 M−1s−1 range. [7] So far, PRDX5 has been shown to be a cytoprotective antioxidant enzyme that inhibits endogenous or exogenous peroxide accumulation. [7]
According to its amino acid sequence, this 2-Cys peroxiredoxin, PRDX5, is the most divergent isoform among mammalian peroxiredoxins, processing only 28% to 30% sequence identity with typical 2-Cys and 1-Cys peroxiredoxins. [9] The divergent amino acid sequence of this atypical peroxiredoxin is reflected in its unique crystal structure. The typical peroxiredoxin is composed of a thioredoxin domain and a C-terminal, whereas PRDX5 has an N-terminal domain and a unique alpha helix replaces a loop structure in the typical thioredoxin domain. [7] In addition, typical 2-Cys or 1-Cys peroxiredoxins are associated as anti-parallel dimers via linkage of two beta-7-strands, whereas a PRDX5 dimer is formed by close contact between an alpha-3-helix of one molecule and an alpha-5-helix from the other molecule. [7]
As a peroxiredoxin, PRDX5 has antioxidative and cytoprotective functions during oxidative stress. Overexpression of human PRDX5 has been shown to inhibit peroxide accumulation induced by TNF-alpha, PDGF, and p53 in NIH3T3 and HeLa cells and reduce cell death by exogenous peroxide in multiple organelles of CHO, HT-22, and human tendon cells. [6] [10] [11] [12] [13] Meanwhile, reduced expression of PRDX5 induces cell susceptibility to oxidative damage and etoposide, doxorubicin, MPP+, and peroxide-induced apoptosis. [14] [15] [16] [17] In addition, expressing human PRDX5 in other organisms or tissues such as yeast, mouse brain, and Xenopus embryos also leads to protection against oxidative stress. [18] [19] [20] PRDX5 in Drosophila melanogaster has been shown to promote longevity in addition to antioxidant activity. [21]
By examining 98 stroke patients, Kunze et al. showed an inverse correlation between stroke progression and PRDX5 concentration, suggesting that plasma PRDX5 can be a potential biomarker of inflammation in acute stroke. [22] In human breast cancer cells, knockdown of transcription factor, GATA1, led to increased expression of PRDX5 and inhibition of apoptosis. [10] A substantial increase in PRDX5 expression has been observed in astrocytes in multiple sclerosis lesion. [23] PRDX5 has also been identified as a candidate risk gene for the inflammatory disease, sarcoidosis. [24]
Transcription factor GATA-binding protein 1 can bind to the PRDX5 gene and lead to increased expression of PRDX5. [10] PRDX5 has been shown to physically interact with PRDX1, PRDX2, PRDX6, SOD1, and PARK7 in at least two independent high-throughput proteomic analyses. [25]
Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants are frequently added to industrial products, such as polymers, fuels, and lubricants, to extend their usable lifetimes. Foods are also treated with antioxidants to forestall spoilage, in particular the rancidification of oils and fats. In cells, antioxidants such as glutathione, mycothiol, or bacillithiol, and enzyme systems like superoxide dismutase, can prevent damage from oxidative stress.
Metallothionein (MT) is a family of cysteine-rich, low molecular weight proteins. They are localized to the membrane of the Golgi apparatus. MTs have the capacity to bind both physiological and xenobiotic heavy metals through the thiol group of its cysteine residues, which represent nearly 30% of its constituent amino acid residues.
In chemistry and biology, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (O2), water, and hydrogen peroxide. Some prominent ROS are hydroperoxide (O2H), superoxide (O2-), hydroxyl radical (OH.), and singlet oxygen. ROS are pervasive because they are readily produced from O2, which is abundant. ROS are important in many ways, both beneficial and otherwise. ROS function as signals, that turn on and off biological functions. They are intermediates in the redox behavior of O2, which is central to fuel cells. ROS are central to the photodegradation of organic pollutants in the atmosphere. Most often however, ROS are discussed in a biological context, ranging from their effects on aging and their role in causing dangerous genetic mutations.
Thioredoxin reductases are enzymes that reduce thioredoxin (Trx). Two classes of thioredoxin reductase have been identified: one class in bacteria and some eukaryotes and one in animals. In bacteria TrxR also catalyzes the reduction of glutaredoxin like proteins known as NrdH. Both classes are flavoproteins which function as homodimers. Each monomer contains a FAD prosthetic group, a NADPH binding domain, and an active site containing a redox-active disulfide bond.
Thioredoxin is a class of small redox proteins known to be present in all organisms. It plays a role in many important biological processes, including redox signaling. In humans, thioredoxins are encoded by TXN and TXN2 genes. Loss-of-function mutation of either of the two human thioredoxin genes is lethal at the four-cell stage of the developing embryo. Although not entirely understood, thioredoxin is linked to medicine through their response to reactive oxygen species (ROS). In plants, thioredoxins regulate a spectrum of critical functions, ranging from photosynthesis to growth, flowering and the development and germination of seeds. Thioredoxins play a role in cell-to-cell communication.
Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal redox state of cells can cause toxic effects through the production of peroxides and free radicals that damage all components of the cell, including proteins, lipids, and DNA. Oxidative stress from oxidative metabolism causes base damage, as well as strand breaks in DNA. Base damage is mostly indirect and caused by the reactive oxygen species generated, e.g., O−
2, OH and H2O2. Further, some reactive oxidative species act as cellular messengers in redox signaling. Thus, oxidative stress can cause disruptions in normal mechanisms of cellular signaling.
Glutathione disulfide (GSSG) is a disulfide derived from two glutathione molecules.
Peroxiredoxins are a ubiquitous family of antioxidant enzymes that also control cytokine-induced peroxide levels and thereby mediate signal transduction in mammalian cells. The family members in humans are PRDX1, PRDX2, PRDX3, PRDX4, PRDX5, and PRDX6. The physiological importance of peroxiredoxins is indicated by their relative abundance. Their function is the reduction of peroxides, specifically hydrogen peroxide, alkyl hydroperoxides, and peroxynitrite.
Transcription factor Jun is a protein that in humans is encoded by the JUN gene. c-Jun, in combination with protein c-Fos, forms the AP-1 early response transcription factor. It was first identified as the Fos-binding protein p39 and only later rediscovered as the product of the JUN gene. c-jun was the first oncogenic transcription factor discovered. The proto-oncogene c-Jun is the cellular homolog of the viral oncoprotein v-jun. The viral homolog v-jun was discovered in avian sarcoma virus 17 and was named for ju-nana, the Japanese word for 17. The human JUN encodes a protein that is highly similar to the viral protein, which interacts directly with specific target DNA sequences to regulate gene expression. This gene is intronless and is mapped to 1p32-p31, a chromosomal region involved in both translocations and deletions in human malignancies.
Nuclear factor erythroid 2-related factor 2 (NRF2), also known as nuclear factor erythroid-derived 2-like 2, is a transcription factor that in humans is encoded by the NFE2L2 gene. NRF2 is a basic leucine zipper (bZIP) protein that may regulate the expression of antioxidant proteins that protect against oxidative damage triggered by injury and inflammation, according to preliminary research. In vitro, NRF2 binds to antioxidant response elements (AREs) in the promoter regions of genes encoding cytoprotective proteins. NRF2 induces the expression of heme oxygenase 1 in vitro leading to an increase in phase II enzymes. NRF2 also inhibits the NLRP3 inflammasome.
Glutathione peroxidase 1, also known as GPx1, is an enzyme that in humans is encoded by the GPX1 gene on chromosome 3. This gene encodes a member of the glutathione peroxidase family. Glutathione peroxidase functions in the detoxification of hydrogen peroxide, and is one of the most important antioxidant enzymes in humans.
Peroxiredoxin-1 is a protein that in humans is encoded by the PRDX1 gene.
Peroxiredoxin-2 is a protein that in humans is encoded by the PRDX2 gene.
Peroxiredoxin-6 is a protein that in humans is encoded by the PRDX6 gene. It is a member of the peroxiredoxin family of antioxidant enzymes.
Thioredoxin-dependent peroxide reductase, mitochondrial is an enzyme that in humans is encoded by the PRDX3 gene. It is a member of the peroxiredoxin family of antioxidant enzymes.
Glutaredoxin 2 (GLRX2) is an enzyme that in humans encoded by the GLRX2 gene. GLRX2, also known as GRX2, is a glutaredoxin family protein and a thiol-disulfide oxidoreductase that maintains cellular thiol homeostasis. This gene consists of four exons and three introns, spanned 10 kilobase pairs, and localized to chromosome 1q31.2–31.3.
Krueppel-like factor 9 is a protein that in humans is encoded by the KLF9 gene. Previously known as Basic Transcription Element Binding Protein 1, Klf9 is part of the Sp1 C2H2-type zinc finger family of transcription factors. Several previous studies showed Klf9-related regulation of animal development, including cell differentiation of B cells, keratinocytes, and neurons. Klf9 is also a key transcriptional regulator for uterine endometrial cell proliferation, adhesion, and differentiation, all factors that are essential during the process of pregnancy and are turned off during tumorigenesis.
Peroxiredoxin-4 is a protein that in humans is encoded by the PRDX4 gene. It is a member of the peroxiredoxin family of antioxidant enzymes.
Thioredoxin, mitochondrial also known as thioredoxin-2 is a protein that in humans is encoded by the TXN2 gene on chromosome 22. This nuclear gene encodes a mitochondrial member of the thioredoxin family, a group of small multifunctional redox-active proteins. The encoded protein may play important roles in the regulation of the mitochondrial membrane potential and in protection against oxidant-induced apoptosis.
Reductive stress (RS) is defined as an abnormal accumulation of reducing equivalents despite being in the presence of intact oxidation and reduction systems. A redox reaction involves the transfer of electrons from reducing agents (reductants) to oxidizing agents (oxidants) and redox couples are accountable for the majority of the cellular electron flow. RS is a state where there are more reducing equivalents compared to reductive oxygen species (ROS) in the form of known biological redox couples such as GSH/GSSG, NADP+/NADPH, and NAD+/NADH. Reductive stress is the counterpart to oxidative stress, where electron acceptors are expected to be mostly reduced. Reductive stress is likely derived from intrinsic signals that allow for the cellular defense against pro-oxidative conditions. There is a feedback regulation balance between reductive and oxidative stress where chronic RS induce oxidative species (OS), resulting in an increase in production of RS, again.