Role of polyamines, their analogs and transglutaminases in biological and clinical perspectives

Methionine: An Indispensable Amino Acid in Cellular Metabolism and Health of Atlantic Salmon

Methionine is an indispensable amino acid with an important role as the main methyl donor in cellular metabolism for both fish and mammals. Metabolization of methionine to the methyl donor S-adenosylmethionine (SAM) has consequence for polyamine, carnitine, phospholipid, and creatine synthesis as well as epigenetic modifications such as DNA- and histone tail methylation. Methionine can also be converted to cysteine and contributes as a precursor for taurine and glutathione synthesis. Moreover, methionine is the start codon for every protein being synthetized and thereby serves an important role in initiating translation. Modern salmon feed is dominated by plant ingredients containing less taurine, carnitine, and creatine than animal-based ingredients. This shift results in competition for SAM due to an increasing need to endogenously synthesize associated metabolites. The availability of methionine has profound implications for various metabolic pathways including allosteric regulation. This necessitates a higher nutritional need to meet the requirement as a methyl donor, surpassing the quantities for protein synthesis and growth. This comprehensive review provides an overview of the key metabolic pathways in which methionine plays a central role as methyl donor and unfolds the implications for methylation capacity, metabolism, and overall health particularly emphasizing the development of fatty liver, oxidation, and inflammation when methionine abundance is insufficient focusing on nutrition for Atlantic salmon (Salmo salar).

Heterologous Expression and Characterization of Tea (Camellia sinensis) Polyamine Oxidase Homologs and Their Involvement in Stresses

Polyamine oxidase (PAO) is a key enzyme maintaining polyamine homeostasis, which affects plant physiological activities. Until now, the gene members and function of PAOs in tea (Camellia sinenesis) have not been fully identified. Here, through the expression in Escherichia coli and Nicotiana benthamiana, we identified six genes annotated as CsPAO in tea genome and transcriptome and determined their enzyme reaction modes and gene expression profiles in tea cultivar 'Yinghong 9'. We found that CsPAO1,2,3 could catalyze spermine, thermospermine, and norspermidine, and CsPAO2,3 could catalyze spermidine in the back-conversion mode, which indicated that the precursor of γ-aminobutyric acid might originate from the oxidation of putrescin but not spermidine. We further investigated the changes of CsPAO activity with temperature and pH and their stability. Kinetic parameters suggested that CsPAO2 was the major PAO modifying polyamine composition in tea, and it could be inactivated by β-hydroxyethylhydrazine and aminoguanidine. Putrescine content and CsPAO2 expression were high in tea flowers. CsPAO2 responded to wound, drought, and salt stress; CsPAO1 might be the main member responding to cold stress; anoxia induced CsPAO3. We conclude that in terms of phylogenetic tree, enzyme characteristics, and expression profile, CsPAO2 might be the dominant CsPAO in the polyamine degradation pathway.

Role of putrescine in ovary and embryo development in fruit bat Cynopterus sphinx during embryonic diapause

The aim of this study was to evaluate the effect of putrescine on ovarian activity and the rate of embryonic development in Cynopterus sphinx during delayed development. The result showed the presence of a rate-limiting enzyme, ornithine decarboxylase-1, in both ovary and utero-embryonic unit of C. sphinx suggests a synthesis of putrescine in these sites. The corpus luteum showed increased, whereas utero-embryonic unit showed decreased production of putrescine during delayed development as compared with the normal development. The bat treated in vivo with putrescine during delayed development showed increase in progesterone and estradiol synthesis, correlated with increased expression of luteinizing hormone receptor, steroidogenic acute receptor protein, and 3β-hydroxysteroid dehydrogenase through extracellular signal-regulated kinase (ERK1/2)-mediated pathway in the ovary; but showed increase in the weight and expression of progesterone receptor (PR), B-cell lymphoma 2, proliferating cell nucleus antigen, and vascular endothelial growth factor proteins in utero-embryonic unit. The in vitro treatment of putrescine showed stimulatory whereas treatment with an inhibitor of putrescine, 2-difluoromethylornithine caused an inhibitory effect on ovarian progesterone synthesis and cell proliferation, and cell survival in the utero-embryonic unit. In conclusion, the putrescine showed two separate roles during embryonic diapause, high concentration of putrescine in the ovary may support corpus luteum and basal synthesis of progesterone, whereas a low level of putrescine causes retarded embryonic development by inhibiting cell proliferation in the utero-embryonic unit. The bat treated with putrescine either directly promotes cell proliferation, cell survival, and angiogenic activities or acts indirectly increasing PR on utero-embryonic unit thereby activating development in delayed embryo in C. sphinx.

15(V/K) kinetic isotope effect and steady-state kinetic analysis for the transglutaminase 2 catalyzed deamidation and transamidation reactions

The Ca²⁺-dependent deamidation and transamidation activities of transglutaminase 2 (TG2) are important to numerous physiological and pathological processes. Herein, we have examined the steady-state kinetics and ¹⁵(V/K) kinetic isotope effects (KIEs) for the TG2-catalyzed deamidation and transamidation of N-Benzyloxycarbonyl-l-Glutaminylglycine (Z-Gln-Gly) using putrescine as the acyl acceptor substrate. Kinetic parameters determined from initial velocity plots are consistent with previously proposed mechanisms. Significant differences in the ¹⁵(V/K) KIEs on NH₃ release determined for the deamidation (0.2%) and the transamidation (2.3%) of Z-Gln-Gly suggest the rate-limiting steps of TG2 active site acylation are dependent on the presence of the acyl acceptor. We propose a plausible mechanistic explanation where substrate-induced conformational changes may play a role in promoting catalysis.

Detection of Free Polyamines in Plants Subjected to Abiotic Stresses by High-Performance Liquid Chromatography (HPLC)

High-performance liquid chromatography (HPLC) is a sensitive, rapid, and accurate technique to detect and characterize various metabolites from plants. The metabolites are extracted with different solvents and eluted with appropriate mobile phases in a designed HPLC program. Polyamines are known to accumulate under abiotic stress conditions in various plant species and thought to provide protection against oxidative stress by scavenging reactive oxygen species. Here, we describe a common method to detect the free polyamines in plant tissues both qualitatively and quantitatively.

Putrescine stimulates the mTOR signaling pathway and protein synthesis in porcine trophectoderm cells

Insufficient placental growth is a major factor contributing to intrauterine growth retardation in mammals. There is growing evidence that putrescine produced from arginine (Arg) and proline via ornithine decarboxylase is a key regulator of angiogenesis, embryogenesis, as well as placental and fetal growth. However, the underlying mechanisms are largely unknown. The present study tested the hypothesis that putrescine stimulates protein synthesis by activating the mechanistic target of rapamycin (mTOR) signaling pathway in porcine trophectoderm cell line 2 cells. The cells were cultured for 2 to 4 days in customized Arg-free Dulbecco modified Eagle Ham medium containing 0, 10, 25, or 50 μM putrescine or 100 μM Arg. Cell proliferation, protein synthesis, and degradation, as well as the abundance of total and phosphorylated mTOR, ribosomal protein S6 kinase 1, and eukaryotic initiation factor 4E-binding protein-1 (4EBP1), were determined. Our results indicate that putrescine promotes cell proliferation and protein synthesis in a dose- and time-dependent manner, which was inhibited by difluoro-methylornithine (an inhibitor of ornithine decarboxylase). Moreover, supplementation of culture medium with putrescine increased the abundance of phosphorylated mTOR and its downstream targets, 4EBP1 and p70 S6K1 proteins. Collectively, these findings reveal a novel and important role for putrescine in regulating the mTOR signaling pathway in porcine placental cells. We suggest that dietary supplementation with or intravenous administration of putrescine may provide a new and effective strategy to improve survival and growth of embryos/fetuses in mammals.

Duplication and diversification of the spermidine/spermine N1-acetyltransferase 1 genes in zebrafish

Spermidine/spermine N(1)-acetyltransferase 1 (Ssat1) is a key enzyme in the polyamine interconversion pathway, which maintains polyamine homeostasis. In addition, mammalian Ssat1 is also involved in many physiological and pathological events such as hypoxia, cell migration, and carcinogenesis. Using cross-genomic bioinformatic analysis in 10 deuterostomes, we found that ssat1 only exists in vertebrates. Comparing with mammalian, zebrafish, an evolutionarily distant vertebrate, contains 3 homologous ssat1 genes, named ssat1a, ssat1b, and ssat1c. All zebrafish homologues could be transcribed and produce active enzymes. Despite the long history since their evolutionary diversification, some features of human SSAT1 are conserved and subfunctionalized in the zebrafish family of Ssat1 proteins. The polyamine-dependent protein synthesis was only found in Ssat1b and Ssat1c, not in Ssat1a. Further study indicated that both 5' and 3' sequences of ssat1b mediate such kind of translational regulation inside the open reading frame (ORF). The polyamine-dependent protein stabilization was only observed in Ssat1b. The last 70 residues of Ssat1b were crucial for its rapid degradation and polyamine-induced stabilization. It is worth noting that only Ssat1b and Ssat1c, but not the polyamine-insensitive Ssat1a, were able to interact with integrin α9 and Hif-1α. Thus, Ssat1b and Ssat1c might not only be a polyamine metabolic enzyme but also simultaneously respond to polyamine levels and engage in cross-talk with other signaling pathways. Our data revealed some correlations between the sequences and functions of the zebrafish family of Ssat1 proteins, which may provide valuable information for studies of their translational regulatory mechanism, protein stability, and physiological functions.