Manganese binding to antioxidant peptides involved in extreme radiation resistance in Deinococcus radiodurans

The ternary complex of Mn2+, synthetic decapeptide DP1 (DEHGTAVMLK), and orthophosphate is a superb antioxidant

Mn2+ coordinated by orthophosphate (Pi), metabolites, or peptides acts as a superoxide dismutase (SOD), and these Mn antioxidant complexes are universally accumulated in extremely radiation-resistant cell types across the tree of life. This behavior prompted design of decapeptide DP1 (DEHGTAVMLK) as a Mn2+ ligand, and development of a highly potent Mn2+-antioxidant (MDP) containing [Pi] = 25 mM, and [DP1] = 3 mM, the ratio found in the radioresistant bacterium Deinococcus radiodurans, with [Mn2+] = 1 mM. MDP is an exceptional antioxidant, both in vitro and in vivo, and has reinvigorated the development of radiation-inactivated whole-cell vaccines. This study investigates the nature of the active Mn2+ complex in MDP. We measure the affinity of DP1 for the substitutionally labile Mn2+ ion using isothermal-titration calorimetry (ITC) and use changes in the Mn2+ solution EPR spectrum to determine affinities of Mn2+ for DP1 and for Pi, and to monitor Mn2+ ligation while titrated with the fixed Pi/DP1 ratio of MDP, 25/3, using ENDOR/ESEEM to characterize DP1 ligation to Mn2+. In parallel, 1H NMR of DP1 was used to monitor binding interactions between Pi and DP1, and DP1 binding to the diamagnetic Ca2+. We report: i) DP1 forms an extremely weak, dynamic Mn2+ complex (Ka ≈ 40 M-1) ii) Mn2+ binds Pi much more strongly (Ka ≈ 390 M-1) as shown previously, but iii) DP1 and Pi jointly bind to Mn2+ in MDP to form a ternary Mn2+ (Pi) (DP1) complex with greater formation-constant than Pi alone (Kaapp ≈ 670 M-1). It is this ternary complex that is the superb antioxidant in MDP.

A Novel Deinococcus Antioxidant Peptide Mitigates Oxidative Stress in Irradiated CHO-K1 Cells

Reactive oxygen species (ROS), byproducts of cellular metabolism and environmental factors, are linked to diseases like cancer and aging. Antioxidant peptides (AOPs) have emerged as effective countermeasures against ROS-induced damage. The Deinococcus genus is well known for its extraordinary resilience to ionizing radiation (IR) and possesses complex antioxidant systems designed to neutralize ROS generated by IR. In this study, we developed four peptides, each containing 9 to 11 amino acids, from the leaderless mRNA (lmRNA) sequences of D. deserti. Lacking a 5' untranslated region, lmRNAs directly initiate protein synthesis, potentially encoding small peptides such as AOPs. Of the four peptides, Ddes-P3 was found to exhibit significant antioxidant capabilities in vitro, effectively scavenging ABTS radicals. Ddes-P3 provided considerable defense against IR-induced oxidative stress in CHO-K1 cells, demonstrating a notable reduction in ROS production and lipid peroxidation. The peptide's potential was highlighted by its ability to enhance cell survival and maintain mitochondrial membrane potential under irradiative stress, suggesting its utility as a nontoxic and effective radioprotector in mitigating radiation-induced cellular damage. This study explores the potential role of lmRNA in synthesizing AOPs within Deinococcus. Identifying lmRNAs that encode AOPs could deepen our understanding of their cellular resistance to oxidative stress and pave the way for creating innovative biotechnological and therapeutic AOPs.

Preliminary Promising Findings for Manganese Chloride as a Novel Radiation Countermeasure Against Acute Radiation Syndrome

INTRODUCTION

Military members and first responders may, at moment's notice, be asked to assist in incidents that may result in radiation exposure such as Operation Tomadachi in which the U.S. Navy provided significant relief for the Fukushima Daiichi Nuclear Reactor accident in Japan after an earthquake and tsunami in 2011. We are also currently facing potential threats from nuclear power plants in the Ukraine should a power disruption to a nuclear plant interfere with cooling or other safety measures. Exposure to high doses of radiation results in acute radiation syndrome (ARS) characterized by symptoms arising from hematopoietic, gastrointestinal, and neurovascular injuries. Although there are mitigators FDA approved to treat ARS, there are currently no FDA-approved prophylactic medical interventions to help protect persons who may need to respond to radiation emergencies. There is strong evidence that manganese (Mn) has radiation protective efficacy as a promising prophylactic countermeasure.

MATERIALS AND METHODS

All animal procedures were approved by the Institutional Animal Care and Use Committee. Male and female B6D2F1J mice, 10 to 11 weeks old, were used for neurotoxicity studies and temporal effects of Mn. Four groups were evaluated: (1) vehicle injection, (2) dose of 4.5 mg/kg for 3 days, (3) dose of 13.5 mg/kg, and (4) sham. Irradiated mice were exposed to 9.5 Gy whole body Co60 γ-radiation. MRI was performed with a high dose of manganese chloride (MnCl2) (150 mg/kg) to assess the distribution of the MnCl2.

RESULTS

The mice have promising survival curves (highest survival-13.5 mg/kg dose over 3 days of MnCl2 at 80% [87% female, 73% male] P = 0.0004). The complete blood count (CBC) results demonstrated a typical hematopoietic response in all of the irradiated groups, followed by mildly accelerated recovery by day 28 in the treated groups. No difference between groups was measured by Rota Rod, DigiGait, and Y-maze. Histologic evaluation of the bone marrow sections in the group given 13.5 mg/kg dose over 3 days had the best return to cellularity at 80%. MRI showed a systemic distribution of MnCl2.

DISCUSSION

The preliminary data suggest that a dose of 13.5 mg/kg of MnCl2 given over 3 days prior to exposure of radiation may have a protective benefit while not exhibiting the neurobehavioral problems. A countermeasure that can prophylactically protect emergency personnel entering an area contaminated with high levels of radiation is needed, especially in light that nuclear accidents are a continued global threat. There is a need for a protective agent with easy long-term storage, easy to transport, easy to administer, and low cost. Histologic evaluation supports the promising effect of MnCl2 in protecting tissue, especially the bone marrow using the dose given over 3 days (4.5 mg/kg per day) of MnCl2.

CONCLUSIONS

Initial experiments show that MnCl2 is a promising safe and effective prophylactic countermeasure against ARS. MRI data support the systemic distribution of MnCl2 which is needed in order to protect multiple tissues in the body. The pathology data in bone marrow and the brain support faster recovery from radiation exposure in the treated animals and decreased organ damage.

Susceptibility of extremophiles to far-UVC light for bioburden reduction in spacecraft assembly facilities

The prevention and reduction of microbial species entering and leaving Earth's biosphere is a critical aspect of planetary protection research. While various decontamination methods exist and are currently utilized for planetary protection purposes, the use of far-UVC light (200-230 nm) as a means for microbial reduction remains underexplored. Unlike conventional germicidal ultraviolet at 254 nm, which can pose a health risk to humans even with small exposure doses, far-UVC light poses minimal health hazard making it a suitable candidate for implementation in occupied areas of spacecraft assembly facilities. This study investigates the efficacy of far-UVC 222-nm light to inactivate bacteria using microbial species which are relevant to planetary protection either in vegetative cell or spore form. All the tested vegetative cells demonstrated susceptibility to 222-nm exposure, although susceptibility varied among the tested species. Notably, Deinococcus radiodurans, a species highly tolerant to extreme environmental conditions, exhibited the most resistance to far-UVC exposure with a dose of 112 mJ/cm2 required for a 1-log reduction in survival. While spore susceptibility was similar across the species tested, Bacillus pumilus spores were the most resistant of the tested spores when analyzed with a bi-exponential cell killing model (D90 of 6.8 mJ/cm2). Overall, these results demonstrate the efficacy of far-UVC light for reducing microbial bioburden to help ensure the success and safety of future space exploration missions.

Antioxidant defense of Deinococcus radiodurans: how does it contribute to extreme radiation resistance?

PURPOSE

Deinococcus radiodurans is an extremely radioresistant bacterium characterized by D10 of 10 kGy, and able to grow luxuriantly under chronic ionizing radiation of 60 Gy/h. The aim of this article is to review the antioxidant system of D. radiodurans and its possible role in the unusual resistance of this bacterium to ionizing radiation.

CONCLUSIONS

The unusual radiation resistance of D. radiodurans has apparently evolved as a side effect of the adaptation of this extremophile to other damaging environmental factors, especially desiccation. The antioxidant proteins and low-molecular antioxidants (especially low-molecular weight Mn2+ complexes and carotenoids, in particular, deinoxanthin), as well as protein and non-protein regulators, are important for the antioxidant defense of this species. Antioxidant protection of proteins from radiation inactivation enables the repair of DNA damage caused by ionizing radiation.

Genetically engineered filamentous phage for bacterial detection using magnetic resonance imaging

Detecting bacterial cells with high specificity in deep tissues is challenging. Optical probes provide specificity, but are limited by the scattering and absorption of light in biological tissues. Conversely, magnetic resonance imaging (MRI) allows unfettered access to deep tissues, but lacks contrast agents for detecting specific bacterial strains. Here, we introduce a biomolecular platform that combines both capabilities by exploiting the modularity of M13 phage to target bacteria with tunable specificity and allow deep-tissue imaging using T1-weighted MRI. We engineered two types of phage probes: one for detecting the phage's natural host, viz., F-pilus expressing E. coli; and the other for detecting a different (F-negative) bacterial target, V. cholerae. We show that these phage sensors generate 3-9-fold stronger T1 relaxation upon recognizing target cells relative to non-target bacteria. We further establish a preliminary proof-of-concept for in vivo applications, by demonstrating that phage-labeled bacteria can be detected in mice using MRI. The framework developed in this study may have potential utility in a broad range of applications, from basic biomedical research to in situ diagnostics, which require methods to detect and track specific bacteria in the context of intact living systems.

Exploring the Specificity of Rationally Designed Peptides Reconstituted from the Cell-Free Extract of Deinococcus radiodurans toward Mn(II) and Cu(II)

A series of five rationally designed decapeptides [DEHGTAVMLK (DP1), THMVLAKGED (DP2), GTAVMLKDEH (Term-DEH), TMVLDEHAKG (Mid-DEH), and DEHGGGGDEH (Bis-DEH)] have been studied for their interactions with Cu(II) and Mn(II) ions. The peptides, constructed including the most prevalent amino acid content found in the cell-free extract of Deinococcus radiodurans (DR), play a fundamental role in the antioxidant mechanism related to its exceptional radioresistance. Mn(II) ions, in complex with these peptides, are found to be an essential ingredient for the DR protection kit. In this work, a detailed characterization of Cu(II) systems was included, because Cu(II)–peptide complexes have also shown remarkable antioxidant properties. All peptides studied contain in their sequence coordinating residues that can bind effectively Mn(II) or Cu(II) ions with high affinity, such as Asp, Glu, and His. Using potentiometric techniques, NMR, EPR, UV–vis, and CD spectroscopies, ESI-MS spectrometry, and molecular model calculations, we explored the binding properties and coordination modes of all peptides toward the two metal ions, were able to make a metal affinity comparison for each metal system, and built a structural molecular model for the most stable Cu(II) and Mn(II) complexes in agreement with experimental evidence.

Five rationally designed decapeptides reconstituted from the cell-free extract of Deinococcus radiodurans have been precisely analyzed in terms of their coordination properties toward Mn(II) and Cu(II). The results provide new insight to enhance our understanding of the impact of metal complexes in the protection of the bacterium from various damaging agents such as ionizing radiation, ultraviolet radiation, and oxidative stress and novel information useful for exploiting this extraordinary ability in future biotechnological applications.

A novel gamma radiation-inactivated sabin-based polio vaccine

A concerted action on the part of international agencies and national governments has resulted in the near-eradication of poliomyelitis. However, both the oral polio vaccine (OPV) and the inactivated polio vaccine (IPV) have deficiencies which make them suboptimal for use after global eradication. OPV is composed of attenuated Sabin strains and stimulates robust immunity, but may revert to neurovirulent forms in the intestine which can be shed and infect susceptible contacts. The majority of IPV products are manufactured using pathogenic strains inactivated with formalin. Upon eradication, the production of large quantities of pathogenic virus will present an increased biosecurity hazard. A logical ideal endgame vaccine would be an inactivated form of an attenuated strain that could afford protective immunity while safely producing larger numbers of doses per unit of virus stock than current vaccines. We report here the development of an ionizing radiation (IR)-inactivated Sabin-based vaccine using a reconstituted Mn-decapeptide (MDP) antioxidant complex derived from the radioresistant bacterium Deinococcus radiodurans. In bacteria, Mn2+-peptide antioxidants protect proteins from oxidative damage caused by extreme radiation exposure. Here we show for the first time, that MDP can protect immunogenic neutralizing epitopes in picornaviruses. MDP protects epitopes in Polio Virus 1 and 2 Sabin strains (PV1-S and PV2-S, respectively), but viral genomic RNA is not protected during supralethal irradiation. IR-inactivated Sabin viruses stimulated equivalent or improved neutralizing antibody responses in Wistar rats compared to the commercially used IPV products. Our approach reduces the biosecurity risk of the current PV vaccine production method by utilizing the Sabin strains instead of the wild type neurovirulent strains. Additionally, the IR-inactivation approach could provide a simpler, faster and less costly process for producing a more immunogenic IPV. Gamma-irradiation is a well-known method of virus inactivation and this vaccine approach could be adapted to any pathogen of interest.

Antioxidative system of Deinococcus radiodurans

Deinococcus radiodurans is famous for its extreme resistance to various stresses such as ionizing radiation (IR), desiccation and oxidative stress. The underlying mechanism of exceptional resistance of this robust bacterium still remained unclear. However, the antioxidative system of D. radiodurans has been considered to be the determinant factor for its unparalleled resistance and protects the proteome during stress, then the DNA repair system and metabolic system exert their functions to restore the cell to normal physiological state. The antioxidative system not only equipped with the common reactive oxygen species (ROS) scavenging enzymes (e.g., catalase and superoxide dismutase) but also armed with a variety of non-enzyme antioxidants (e.g., carotenoids and manganese species). And the small manganese complexes play an important role in the antioxidative system of D. radiodurans. Recent studies have characterized several regulators (e.g., PprI and PprM) in D. radiodurans, which play critical roles in the protection of the bacteria from various stresses. In this review, we offer a panorama of the progress regarding the characteristics of the antioxidative system in D. radiodurans and its application in the future.

A Model for Manganese interaction with Deinococcus radiodurans proteome network involved in ROS response and defense

A complex network of regulatory proteins takes part in the mechanism underlying the radioresistance of Deinoccocus radiodurans bacterium (DR). The interaction of Mn(II) ions with DR-proteins and peptides seems to be responsible for proteins protection from oxidative damage induced by Reactive Oxygen Species during irradiation. In the present work we describe a combined approach of bioinformatic strategies based on structural data and annotation to predict the Mn(II)-binding proteins encoded by the genome of DR and, in parallel, the same predictions for other bacteria were performed; the comparison revealed that, in most of the cases, the content of Mn(II)-binding proteins is significantly higher in radioresistant than in radiosensitive bacteria. Moreover, we report the in silico protein-protein interaction network of the putative Mn(II)-proteins, remodeled in order to enhance the knowledge about the impact of Mn-binding proteins in DR ability to protect also DNA from various damaging agents such as ionizing radiation, UV radiation and oxidative stress.

para-Aminosalicylic acid in the treatment of manganese toxicity. Complexation of Mn2+ with 4-amino-2-hydroxybenzoic acid and its N-acetylated metabolite

Manganese excess can induce in humans neurological disorders known as manganism.

Ni(II) interaction with a peptide model of the human TLR4 ectodomain

Ni(II) stimulates innate immunity via the direct binding to human Toll Like Receptor 4 (hTLR4), the bacterial lypopolysaccharide receptor. The binding is specific for humans and causes nickel contact allergy. The protein sequence analysis of hTLR4 revealed that the ectodomain, the region supposed to coordinate the metal ions, contains a histidine-rich motif that is not conserved among all organisms. To elucidate the role of each histidine residue on the protein-nickel binding, we examined the formation of Ni(II) complexes with the model peptide NH₂-FQHSNRKQMSERSVFRSRRNRIYRDISHTHTR-COO^-, which encompasses the sequence 429-460 of hTLR4. The amino acid sequence of the peptide has been modified by the substitution of some selected lipophilic residues (Leu and Phe) with hydrophilic residues (Arg), aiming at increasing the peptide hydro solubility of the protein fragment. Potentiometric, ultraviolet-visible (UV-vis), nuclear magnetic resonance (NMR) and circular dichroism (CD) measurements demonstrate that the non-conserved histidines in the ectodomain cooperate in metal coordination and consequently enable the activation of the molecular mechanism of nickel hypersensitivity reaction.

Across the tree of life, radiation resistance is governed by antioxidant Mn2+, gauged by paramagnetic resonance

Despite concerted functional genomic efforts to understand the complex phenotype of ionizing radiation (IR) resistance, a genome sequence cannot predict whether a cell is IR-resistant or not. Instead, we report that absorption-display electron paramagnetic resonance (EPR) spectroscopy of nonirradiated cells is highly diagnostic of IR survival and repair efficiency of DNA double-strand breaks (DSBs) caused by exposure to gamma radiation across archaea, bacteria, and eukaryotes, including fungi and human cells. IR-resistant cells, which are efficient at DSB repair, contain a high cellular content of manganous ions (Mn²⁺) in high-symmetry (H) antioxidant complexes with small metabolites (e.g., orthophosphate, peptides), which exhibit narrow EPR signals (small zero-field splitting). In contrast, Mn²⁺ ions in IR-sensitive cells, which are inefficient at DSB repair, exist largely as low-symmetry (L) complexes with substantially broadened spectra seen with enzymes and strongly chelating ligands. The fraction of cellular Mn²⁺ present as H-complexes (H-Mn²⁺), as measured by EPR of live, nonirradiated Mn-replete cells, is now the strongest known gauge of biological IR resistance between and within organisms representing all three domains of life: Antioxidant H-Mn²⁺ complexes, not antioxidant enzymes (e.g., Mn superoxide dismutase), govern IR survival. As the pool of intracellular metabolites needed to form H-Mn²⁺ complexes depends on the nutritional status of the cell, we conclude that IR resistance is predominantly a metabolic phenomenon. In a cross-kingdom analysis, the vast differences in taxonomic classification, genome size, and radioresistance between cell types studied here support that IR resistance is not controlled by the repertoire of DNA repair and antioxidant enzymes.