Structure-Affinity Relationships of Reversible Proline Analog Inhibitors Targeting Proline Dehydrogenase

Proline dehydrogenase (PRODH) catalyzes the first step of proline catabolism, the FAD-dependent oxidation of L-proline to Δ1-pyrroline-5-carboxylate. PRODH plays a central role in the metabolic rewiring of cancer cells, which...

Proline metabolism and redox; maintaining a balance in health and disease

Proline is a non-essential amino acid with key roles in protein structure/function and maintenance of cellular redox homeostasis. It is available from dietary sources, generated de novo within cells, and released from protein structures; a noteworthy source being collagen. Its catabolism within cells can generate ATP and reactive oxygen species (ROS). Recent findings suggest that proline biosynthesis and catabolism are essential processes in disease; not only due to the role in new protein synthesis as part of pathogenic processes but also due to the impact of proline metabolism on the wider metabolic network through its significant role in redox homeostasis. This is particularly clear in cancer proliferation and metastatic outgrowth. Nevertheless, the precise identity of the drivers of cellular proline catabolism and biosynthesis, and the overall cost of maintaining appropriate balance is not currently known. In this review, we explore the major drivers of proline availability and consumption at a local and systemic level with a focus on cancer. Unraveling the main factors influencing proline metabolism in normal physiology and disease will shed light on new effective treatment strategies.

Expression of Arabidopsis Ornithine Aminotransferase (AtOAT) Encoded Gene Enhances Multiple Abiotic Stress Tolerances in Wheat

Key Message The drought and salt tolerances of wheat were enhanced by ectopic expression of the Arabidopsis ornithine aminotransferase (AtOAT) encoded gene. The OAT was confirmed to play a role in proline biosynthesis in wheat.Abstract Proline (Pro) accumulation is a common response to both abiotic and biotic stresses in plants. Ornithine aminotransferase (OAT) is pyridoxal-5-phosphate dependent enzyme involved in plant proline biosynthesis. During stress condition, proline is synthesized via glutamate and ornithine pathways. The OAT is the key enzyme in ornithine pathway. In this study, an OAT gene AtOAT from Arabidopsis was expressed in wheat for its functional characterization under drought, salinity and heat stress conditions. We found that the expression of AtOAT enhanced the drought and salt stress tolerances of wheat by increasing the proline content and peroxidase activity. In addition, it was confirmed that the expression of AtOAT also played a partial tolerance to heat stress in the transgenic wheat plants. Moreover, quantitative real-time PCR (qRT-PCR) analysis showed that the transformation of AtOAT up-regulated the expression of the proline biosynthesis associated genes TaOAT, TaP5CS, and TaP5CR, and down-regulated that of the proline catabolism related gene TaP5CDH in the transgenic plants under stress conditions. Moreover, the genes involved in ornithine pathway (Orn-OAT-P5C/GSA-P5CR-Pro) were up-regulated along with the up-regulation of those genes involved in glutamate pathway (Glu-P5CS-P5C/GSA-P5CR-Pro). Therefore, we concluded that the expression of AtOAT enhanced wheat abiotic tolerance via modifying the proline biosynthesis by up-regulating the expression of the proline biosynthesis associated genes and down-regulating that of the proline catabolic gene under stresses condition.

Osmotolerance of т4 generation monocotyledonous and dicotyledonous plants with suppressed expression of proline catabolism gene

Analysis of transgene function retention in seed generation (Т4) of genetically modified plants of maize, wheat and sunflower was carried out. It was shown that about 80–85 % of seeds of plants created by the biotechnological method had the ability to germinate under conditions of water deficiency and salinization, while in plants of the original forms this index was 20—28 %. Variability in transgene expression among individual variants of the seed generation of genetically modified forms was noted. Almost 65 % of Т4 seedlings of corn and wheat withstood the conditions of super hard osmotic stress created by adding 0,8 M manite to the culture medium, which was lethal to the original forms. Progenies of transgenic plants were also characterized by an increased level of resistance to drought created by the water cessation, which was manifested in the indices of growth processes. At the stage of restoration after the action of prolonged dehydration, the biotechnological plants of sunflower were 17 cm higher than the original form and had 1.5 times larger biomass. Maintaining the viability of genetically modified plants under hard stressful conditions was associated with an increase in the level of free L-proline (Pro). Genetically modified plants had 1.5—2 times higher Pro content compared to the original form both under normal moisture supply and under its deficiency, which may result from partial suppression of the proline dehydrogenase (PDH, pdh) gene. It was found that under normal growth conditions, the activity of the PDH enzyme in transgenic Т4 maize and sunflower seedlings was almost 3 times lower than in the original forms, while for wheat, this difference was 1.6 times. The tendency to lower relatively to control PDH activity in the Т4 generation of the studied representatives of transgenic monocotyledonous and dicotyledonous plants was observed at all stages of growth.

Loss of flavin adenine dinucleotide (FAD) impairs sperm function and male reproductive advantage in C. elegans

Exposure to environmental stress is clinically established to influence male reproductive health, but the impact of normal cellular metabolism on sperm quality is less well-defined. Here we show that impaired mitochondrial proline catabolism, reduces energy-storing flavin adenine dinucleotide (FAD) levels, alters mitochondrial dynamics toward fusion, and leads to age-related loss of sperm quality (size and activity), which diminishes competitive fitness of the animal. Loss of the 1-pyrroline-5-carboxylate dehydrogenase enzyme alh-6 that catalyzes the second step in mitochondrial proline catabolism leads to premature male reproductive senescence. Reducing the expression of the proline catabolism enzyme alh-6 or FAD biosynthesis pathway genes in the germline is sufficient to recapitulate the sperm-related phenotypes observed in alh-6 loss-of-function mutants. These sperm-specific defects are suppressed by feeding diets that restore FAD levels. Our results define a cell autonomous role for mitochondrial proline catabolism and FAD homeostasis on sperm function and specify strategies to pharmacologically reverse these defects.

Leaf status and environmental signals jointly regulate proline metabolism in winter oilseed rape

Proline metabolism is an essential component of plant adaptation to multiple environmental stress conditions that is also known to participate in specific developmental phases, particularly in reproductive organs. Recent evidence suggested a possible role for proline catabolism in Brassica napus for nitrogen remobilization processes from source leaves at the vegetative stage. Here, we investigate transcript levels of Δ1-PYRROLINE-5-CARBOXYLATE SYNTHASE (P5CS) and PROLINE DEHYDROGENASE (ProDH) genes at the vegetative stage with respect to net proline biosynthesis and degradation fluxes in leaves having a different sink/source balance. We showed that the underexpression of three P5CS1 genes in source leaves was accompanied by a reduced commitment of de novo assimilated 15N towards proline biosynthesis and an overall depletion of free proline content. We found that the expression of ProDH genes was strongly induced by carbon starvation conditions (dark-induced senescence) compared with early senescing leaves. Our results suggested a role for proline catabolism in B. napus, but acting only at a late stage of senescence. In addition, we also identified some P5CS and ProDH genes that were differentially expressed during multiple processes (leaf status, dark to light transition, and stress response).