Identification and characterization of a putative arginine kinase homolog from Myxococcus xanthus required for fruiting body formation and cell differentiation

A comprehensive review of arginine kinase proteins: What we need to know?

The enzyme arginine kinase (AK), EC 2.7.3.3, catalyzes the reversible phosphorylation of arginine with adenosine triphosphate, forming phosphoarginine, which acts as an energy reservoir due to its high-energy phosphate content that can be rapidly transferred to ADP for ATP renewal. It has been proposed that AK should be associated with some ATP biosynthesis mechanisms, such as glycolysis and oxidative phosphorylation. Arginine kinase is an analogue of creatine kinase found in vertebrates. A literature survey has recovered the physicochemical and structural characteristics of AK. This enzyme is widely distributed in invertebrates such as protozoa, bacteria, porifera, cnidaria, mollusca, and arthropods. Arginine kinase may be involved in the response to abiotic and biotic stresses, being up regulated in several organisms and controlling energy homeostasis during environmental changes. Additionally, phosphoarginine plays a role in providing energy for the transport of protozoa, the beating of cilia, and flagellar movement, processes that demand continuous energy. Arginine kinase is also associated with allergies to shellfish and arthropods, such as shrimp, oysters, and cockroaches. Phenolic compounds such as resveratrol, which decrease AK activity by 50 % in Trypanosoma cruzi, inhibit the growth of the epimastigote and trypomastigote forms, making them a significant target for the development of medications for Chagas Disease treatment.

Beyond mitochondria: Alternative energy-producing pathways from all strata of life

It is well-established that mitochondria are the powerhouses of the cell, producing adenosine triphosphate (ATP), the universal energy currency. However, the most significant strengths of the electron transport chain (ETC), its intricacy and efficiency, are also its greatest downfalls. A reliance on metal complexes (FeS clusters, hemes), lipid moities such as cardiolipin, and cofactors including alpha-lipoic acid and quinones render oxidative phosphorylation vulnerable to environmental toxins, intracellular reactive oxygen species (ROS) and fluctuations in diet. To that effect, it is of interest to note that temporal disruptions in ETC activity in most organisms are rarely fatal, and often a redundant number of failsafes are in place to permit continued ATP production when needed. Here, we highlight the metabolic reconfigurations discovered in organisms ranging from parasitic Entamoeba to bacteria such as pseudomonads and then complex eukaryotic systems that allow these species to adapt to and occasionally thrive in harsh environments. The overarching aim of this review is to demonstrate the plasticity of metabolic networks and recognize that in times of duress, life finds a way.

Broad-complex transcription factor mediates opposing hormonal regulation of two phylogenetically distant arginine kinase genes in Tribolium castaneum

The phosphoarginine-arginine kinase shuttle system plays a critical role in maintaining insect cellular energy homeostasis. Insect molting and metamorphosis are coordinated by fluctuations of the ecdysteroid and juvenile hormone. However, the hormonal regulation of insect arginine kinases remain largely elusive. In this report, we comparatively characterized two arginine kinase genes, TcAK1 and TcAK2, in Tribolium castaneum. Functional analysis using RNAi showed that TcAK1 and TcAK2 play similar roles in adult fertility and stress response. TcAK1 was detected in cytoplasm including mitochondria, whereas TcAK2 was detected in cytoplasm excluding mitochondria. Interestingly, TcAK1 expression was negatively regulated by 20-hydroxyecdysone and positively by juvenile hormone, whereas TcAK2 was regulated by the opposite pattern. RNAi, dual-luciferase reporter assays and electrophoretic mobility shift assay further revealed that the opposite hormonal regulation of TcAK1 and TcAK2 was mediated by transcription factor Broad-Complex. Finally, relatively stable AK activities were observed during larval-pupal metamorphosis, which was generally consistent with the constant ATP levels. These results provide new insights into the mechanisms underlying the ATP homeostasis in insects by revealing opposite hormonal regulation of two phylogenetically distant arginine kinase genes.

Zhang et al. characterize the functions of two distinct arginine kinase genes in flour beetles. Using RNA interference and electophoretic mobility shift assays, they identify Broad-Complex transcription factor as the mediator of opposing hormonal regulation in these genes.

Gene silencing by RNAi via oral delivery of dsRNA by bacteria in the South American tomato pinworm, Tuta absoluta

BACKGROUND

RNA interference (RNAi) has been evaluated in several insect pests as a novel strategy to be included in integrated pest management. Lepidopterans are recognized to be recalcitrant to gene silencing by RNAi. As such, double-stranded RNA (dsRNA) delivery needs to be adjusted to assure its stability until it reaches the target gene transcript for silencing. Gene silencing by RNAi offers the potential to be used in the control of Tuta absoluta (Meyrick), one of the main insect pests of tomato (Solanum lycopersicum) worldwide. Here, we tested the delivery of dsRNA expressed in Escherichia coli HT115(DE3) and supplied to larvae in an artificial diet by screening target genes for silencing. We tested six target genes: juvenile hormone inducible protein (JHP); juvenile hormone epoxide hydrolase protein (JHEH); ecdysteroid 25-hydroxylase (PHM); chitin synthase A (CHI); carboxylesterase (COE); and arginine kinase (AK).

RESULTS

Based on larval mortality, the duration of the larval stage in days, pupal weight, and the accumulation of the target gene transcript, we demonstrated the efficacy of bacterial dsRNA delivery for the functional effects on larval development. Providing dsRNA targeted to JHP, CHI, COE and AK by bacteria led to a significant decrease in transcript accumulation and an increase in larval mortality.

CONCLUSION

Bacteria expressing dsRNA targeting essential T. absoluta genes supplied in artificial diet are efficient to screen RNAi target-genes. The oral delivery of dsRNA by bacteria is a novel potential alternative for the control of T. absoluta based on RNAi. © 2019 Society of Chemical Industry.

Protein post-translational modifications in bacteria

Over the past decade the number and variety of protein post-translational modifications that have been detected and characterized in bacteria have rapidly increased. Most post-translational protein modifications occur in a relatively low number of bacterial proteins in comparison with eukaryotic proteins, and most of the modified proteins carry low, substoichiometric levels of modification; therefore, their structural and functional analysis is particularly challenging. The number of modifying enzymes differs greatly among bacterial species, and the extent of the modified proteome strongly depends on environmental conditions. Nevertheless, evidence is rapidly accumulating that protein post-translational modifications have vital roles in various cellular processes such as protein synthesis and turnover, nitrogen metabolism, the cell cycle, dormancy, sporulation, spore germination, persistence and virulence. Further research of protein post-translational modifications will fill current gaps in the understanding of bacterial physiology and open new avenues for treatment of infectious diseases.

Bacterial arginine kinases have a highly skewed distribution within the proteobacteria

Phosphagen kinases (PKs) are known to be distributed throughout the animal kingdom, but have recently been discovered in some protozoan and bacterial species. A recent search of the available bacterial genomes revealed 49 unique sequences that appear to code for an arginine kinase (AK). The distribution of sequences was highly skewed with thirty nine out the forty nine sequences being found in six Proteobacteria classes (α, β, δ, γ, ε, and ζ) which represented 46.6% of the 61,335 bacterial genomes available at JGI-IMG/M website. Moreover, twenty one of the unique and metagenome bAK sequences identified were from δ-Proteobacteria despite these representing only 0.88% of the total genomes available. Phylogenetic analyses revealed that the bacterial AK sequences were interpersed between basal species such as cnidarians, sponges and protozoa, displaying an unstable clustering that was dependent upon the parameters chosen for phylogenetic analysis. Three of these putative bacterial AK genes were cloned into the pET45 expression vector, expressed, and biochemically confirmed to be capable of phosphorylating arginine using ATP. Results of the kinetic analyses of the putative bAKs from Ahrensia, D. autotrophicum, and O. profundus show that the catalytic efficiencies with respect to arginine for each enzyme, measured at 10⁴-10⁵ M^-1 s^-1, fall within the range expected for competent arginine kinases.

Natural Products Containing 'Rare' Organophosphorus Functional Groups

Phosphorous-containing molecules are essential constituents of all living cells. While the phosphate functional group is very common in small molecule natural products, nucleic acids, and as chemical modification in protein and peptides, phosphorous can form P⁻N (phosphoramidate), P⁻S (phosphorothioate), and P⁻C (e.g., phosphonate and phosphinate) linkages. While rare, these moieties play critical roles in many processes and in all forms of life. In this review we thoroughly categorize P⁻N, P⁻S, and P⁻C natural organophosphorus compounds. Information on biological source, biological activity, and biosynthesis is included, if known. This review also summarizes the role of phosphorylation on unusual amino acids in proteins (N- and S-phosphorylation) and reviews the natural phosphorothioate (P⁻S) and phosphoramidate (P⁻N) modifications of DNA and nucleotides with an emphasis on their role in the metabolism of the cell. We challenge the commonly held notion that nonphosphate organophosphorus functional groups are an oddity of biochemistry, with no central role in the metabolism of the cell. We postulate that the extent of utilization of some phosphorus groups by life, especially those containing P⁻N bonds, is likely severely underestimated and has been largely overlooked, mainly due to the technological limitations in their detection and analysis.

Built to bind: biosynthetic strategies for the formation of small-molecule protease inhibitors

The discovery and characterization of natural product protease inhibitors has inspired the development of numerous pharmaceutical agents.

The proteome map of the escamolera ant (Liometopum apiculatum Mayr) larvae reveals immunogenic proteins and several hexamerin proteoforms

The larvae of escamolera ant (Liometopum apiculatum Mayr) have been considered a delicacy since Pre-Hispanic times. The increased demand for this stew has led to massive collection of ant nests. Yet biological aspects of L. apiculatum larvae remain unknown, and mapping the proteome of this species is important for understanding its biological characteristics. Two-dimensional gel electrophoresis (2-DE) followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was used to characterize the larvae proteome profile. From 380 protein spots analyzed, 174 were identified by LC-MS/MS and homology search against the Hymenoptera subset of the NCBInr protein database using the Mascot search engine. Peptide de novo sequencing and homology-based alignment allowed the identification of 36 additional protein spots. Identified proteins were classified by cellular location, molecular function, and biological process according to the Gene Ontology annotation. Immunity- and defense-related proteins were identified including PPIases, FK506, PEBP, and chitinases. Several hexamerin proteoforms were identified and the cDNA of the most abundant protein detected in the 2-DE map was isolated and characterized. L. apiculatum hexamerin (LaHEX, GeneBank accession no. MH256667) contains an open reading frame of 2199 bp encoding a polypeptide of 733 amino acid residues with a calculated molecular mass of 82.41 kDa. LaHEX protein is more similar to HEX110 than HEX70 from Apis mellifera. Down-regulation of LaHEX was observed throughout ant development. This work represents the first proteome map as well as the first hexamerin characterized from L. apiculatum larvae.

The toxic effect of sodium fluoride on Spodoptera frugiperda 9 cells and differential protein analysis following NaF treatment of cells

Accumulation of excess fluoride has a destructive effect on the environment, endangering human health, affecting organism growth and development, and leading to damage to the biological chain, thereby affecting ecological environment balance. In recent years, numerous studies focused on the molecular mechanisms associated with fluoride toxicity; however, fluoride-toxicity mechanisms in insect cells remain unclear. This study explored the toxic impact of sodium fluoride (NaF) on Spodoptera frugiperda 9 (Sf9) insect cells. High concentrations of NaF (10^-4 M, 10^-3 M and 10^-2 M) resulted in cell enlargement, cell membrane blurring and breakage, and release of cellular contents. Dose-response curves indicated that NaF-specific inhibition rates on Sf9-cell activity increased along with increases in NaF concentration, with a half-inhibitory concentration (IC₅₀) for NaF of 5.919 × 10^-3 M at 72 h. Compared with controls, the percentages of early and late apoptotic and necrotic cells clearly increased based on observed increases in NaF concentrations. Two-dimensional gel electrophoresis combined with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to detect differentially expressed proteins in Sf9 cells treated with IC₅₀ NaF, identifying 17 proteins, seven of which were upregulated and 10 downregulated. These results demonstrated that Sf9 cells showed signs of NaF-mediated toxicity through alterations in cell morphology, apoptosis rates, and protein expression.

RNA interference as a gene silencing tool to control Tuta absoluta in tomato (Solanum lycopersicum)

RNA interference (RNAi), a gene-silencing mechanism that involves providing double-stranded RNA molecules that match a specific target gene sequence, is now widely used in functional genetic studies. The potential application of RNAi-mediated control of agricultural insect pests has rapidly become evident. The production of transgenic plants expressing dsRNA molecules that target essential insect genes could provide a means of specific gene silencing in larvae that feed on these plants, resulting in larval phenotypes that range from loss of appetite to death. In this report, we show that the tomato leafminer ( Tuta absoluta ), a major threat to commercial tomato production, can be targeted by RNAi. We selected two target genes (Vacuolar ATPase-A and Arginine kinase) based on the RNAi response reported for these genes in other pest species. In view of the lack of an artificial diet for T. absoluta, we used two approaches to deliver dsRNA into tomato leaflets. The first approach was based on the uptake of dsRNA by leaflets and the second was based on "in planta-induced transient gene silencing" (PITGS), a well-established method for silencing plant genes, used here for the first time to deliver in planta-transcribed dsRNA to target insect genes. Tuta absoluta larvae that fed on leaves containing dsRNA of the target genes showed an ∼60% reduction in target gene transcript accumulation, an increase in larval mortality and less leaf damage. We then generated transgenic 'Micro-Tom' tomato plants that expressed hairpin sequences for both genes and observed a reduction in foliar damage by T. absoluta in these plants. Our results demonstrate the feasibility of RNAi as an alternative method for controlling this critical tomato pest.

The modulation of haemolymph arginine kinase on the extracellular ATP induced bactericidal immune responses in the Pacific oyster Crassostrea gigas

Arginine kinase is an important phosphagen kinase (PK) which plays an essential role in ATP buffering systems in invertebrates. In the present study, an arginine kinase (designated CgAK) was isolated by the lipopolysaccharide (LPS) affinity chromatography from the haemolymph of Crassostrea gigas. CgAK could directly bind to LPS in a concentration-dependent manner with the dissociation constant (Kd) of 2.46 × 10(-6) M. The interaction with LPS significantly decreased the ATP hydrolytic activity of CgAK, which in turn lead to the accumulation of ATP in vitro. The extracellular ATP stimulation could induce Ca(2+) influx, reactive oxygen species (ROS) production, and the release of lysosomal enzyme in the cellular immune response. In addition, ATP stimulation provoked the bactericidal activity towards Escherichia coli, and the scavenging ROS with N-acetyl-l-cysteine (NAC) abrogated the bactericidal activity, indicating that ATP stimulation could induce ROS-dependent antimicrobial activity in haemocytes. Collectively, the results demonstrated that the haemolymph CgAK could serve as an important purinergic regulator to modulate extracellular ATP, which might further have an important effect on the purinergic signaling-activated innate immune response of oyster.

Exploring the diversity of protein modifications: special bacterial phosphorylation systems

Protein modifications not only affect protein homeostasis but can also establish new cellular protein functions and are important components of complex cellular signal sensing and transduction networks. Among these post-translational modifications, protein phosphorylation represents the one that has been most thoroughly investigated. Unlike in eukarya, a large diversity of enzyme families has been shown to phosphorylate and dephosphorylate proteins on various amino acids with different chemical properties in bacteria. In this review, after a brief overview of the known bacterial phosphorylation systems, we focus on more recently discovered and less widely known kinases and phosphatases. Namely, we describe in detail tyrosine- and arginine-phosphorylation together with some examples of unusual serine-phosphorylation systems and discuss their potential role and function in bacterial physiology, and regulatory networks. Investigating these unusual bacterial kinase and phosphatases is not only important to understand their role in bacterial physiology but will help to generally understand the full potential and evolution of protein phosphorylation for signal transduction, protein modification and homeostasis in all cellular life.

Characterization of the arginine kinase isoforms in Caenorhabditis elegans

Phosphagen kinases (PKs) are well-studied enzymes involved in energy homeostasis in a wide range of animal, protozoan, and even some bacterial species. Recent genome efforts have allowed comparative work on the PKs to extend beyond the biochemistry of individual proteins to the comparative cellular physiology and examining of the role of all PK family members in an organism. The sequencing of the Caenorhabditis elegans genome and availability of sophisticated genetic tools within that system affords the opportunity to conduct a detailed physiological analysis of the PKs from a well known invertebrate for comparison with the extensive work conducted on vertebrate systems. As a first step in this effort we have carried out a detailed molecular genetic and biochemical characterization of the PKs in C. elegans. Our results reveal that C. elegans has five PK genes encoding arginine kinases that range in catalytic efficiency (kcat/KM(Arg)) from (3.1±0.6)×10(4) to (9±4)×10(5) M(-1) s(-1). This range is generally within the range seen for arginine kinases from a variety of species. Our molecular genetic and phylogenetic analysis reveals that the gene family has undergone extensive intron loss and gain within the suborder Rhabditina. In addition, within C. elegans we find evidence of gene duplication and loss. The analysis described here for the C. elegans AKs represents one of the most complete biochemical and molecular genetic analysis of a PK family within a genetically tractable invertebrate system and opens up the possibility of conducting detailed physiological comparisons with vertebrate systems using the sophisticated tools available with this model invertebrate system.

Two arginine kinases of Tetrahymena pyriformis: characterization and localization

Two cDNAs, one coding a typical 40-kDa arginine kinase (AK1) and the other coding a two-domain 80-kDa enzyme (AK2), were isolated from ciliate Tetrahymena pyriformis, and their recombinant enzymes were successfully expressed in Escherichia coli. Both enzymes had an activity comparable to those of typical invertebrate AKs. Interestingly, the amino acid sequence of T. pyriformis AK1, but not AK2, had a distinct myristoylation signal sequence at the N-terminus, suggesting that 40-kDa AK1 targets the membrane. Moreover, Western blot analysis showed that the AK1 is mainly localized in the ciliary fraction. Based on these results, we discuss the phosphoarginine shuttle, which enables a continuous energy flow to dynein for ciliary movement in T. pyriformis, and the role of AK1 in this model.

Characterization of a putative oomycete taurocyamine kinase: Implications for the evolution of the phosphagen kinase family

Phosphagen kinases (PKs) are known to be distributed throughout the animal kingdom, but have recently been discovered in some protozoan and bacterial species. Within animal species, these enzymes play a critical role in energy homeostasis by catalyzing the reversible transfer of a high-energy phosphoryl group from Mg⋅ATP to an acceptor molecule containing a guanidinium group. In this work, a putative PK gene was identified in the oomycete Phytophthora sojae that was predicted, based on sequence homology, to encode a multimeric hypotaurocyamine kinase. The recombinant P. sojae enzyme was purified and shown to catalyze taurocyamine phosphorylation efficiently (kcat/KM (taurocyamine) = 2 × 10(5) M(-1) s(-1)) and glycocyamine phosphorylation only weakly (kcat/KM (glycocyamine) = 2 × 10(2) M(-1) s(-1)), but lacked any observable kinase activity with the more ubiquitous guanidinium substrates, creatine or arginine. Additionally, the enzyme was observed to be dimeric but lacked cooperativity between the subunits in forming a transition state analog complex. These results suggest that protozoan PKs may exhibit more diversity in substrate specificity than was previously thought.

A novel taurocyamine kinase found in the protist Phytophthora infestans

Phosphagen kinase (PK), which is typically in the form of creatine kinase (CK; EC 2.7.3.2) in vertebrates or arginine kinase (AK; EC 2.7.3.3) in invertebrates, plays a key role in ATP buffering systems of tissues and nerves that display high and variable rates of ATP turnover. The enzyme is also found with intermittent occurrence as AK in unicellular organisms, protist and bacteria species, suggesting an ancient origin of AK. Through a database search, we identified two novel PK genes, coding 40- and 80-kDa (contiguous dimer) enzymes in the protist Phytophthora infestans. Both enzymes showed strong activity for taurocyamine and, in addition, we detected taurocyamine in cell extracts of P. infestans. Thus, the enzyme was identified to be taurocyamine kinase (TK; EC 2.7.3.4). This was the first phosphagen kinase, other than AK, to be found in unicellular organisms. Their position on the phylogenetic tree indicates that P. infestans TKs evolved uniquely at an early stage of evolution. Occurrence of TK in protists suggests that PK enzymes show flexible substrate specificity.