Substrate channeling in proline metabolism

Arentson, Benjamin W.; Sanyal, Nikhilesh; Becker, Donald F.

doi:10.2741/3932

Cited by 55 publications

(60 citation statements)

References 70 publications

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“…P5CS is a bifunctional adenosine triphosphate (ATP) and an NAD(P)H-dependent enzyme in higher eukaryotes that displays glutamate kinase (GK) and c-glutamyl phosphate reductase (GPR) activities (49,110). In primitive organisms such as bacteria and yeast, GK and GPR are monofunctional enzymes (6,94). The structure of bifunctional P5CS has not been reported, but individual structures of GK and GPR are available from bacteria (79,89).…”

Section: Proline Metabolic Enzymesmentioning

confidence: 99%

Proline Mechanisms of Stress Survival

Liang

Zhang

Natarajan

et al. 2013

Antioxidants & Redox Signaling

925

576

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Significance: The imino acid proline is utilized by different organisms to offset cellular imbalances caused by environmental stress. The wide use in nature of proline as a stress adaptor molecule indicates that proline has a fundamental biological role in stress response. Understanding the mechanisms by which proline enhances abiotic/biotic stress response will facilitate agricultural crop research and improve human health. Recent Advances: It is now recognized that proline metabolism propels cellular signaling processes that promote cellular apoptosis or survival. Studies have shown that proline metabolism influences signaling pathways by increasing reactive oxygen species (ROS) formation in the mitochondria via the electron transport chain. Enhanced ROS production due to proline metabolism has been implicated in the hypersensitive response in plants, lifespan extension in worms, and apoptosis, tumor suppression, and cell survival in animals. Critical Issues: The ability of proline to influence disparate cellular outcomes may be governed by ROS levels generated in the mitochondria. Defining the threshold at which proline metabolic enzyme expression switches from inducing survival pathways to cellular apoptosis would provide molecular insights into cellular redox regulation by proline. Are ROS the only mediators of proline metabolic signaling or are other factors involved? Future Directions: New evidence suggests that proline biosynthesis enzymes interact with redox proteins such as thioredoxin. An important future pursuit will be to identify other interacting partners of proline metabolic enzymes to uncover novel regulatory and signaling networks of cellular stress response. Antioxid. Redox Signal. 19, 998-1011.

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Section: Proline Metabolic Enzymesmentioning

confidence: 99%

Proline Mechanisms of Stress Survival

Liang

Zhang

Natarajan

et al. 2013

Antioxidants & Redox Signaling

925

576

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“…␥-Glutamyl phosphate is believed to be channeled from the active site of ProB (glutamyl kinase) to the active site of ProA (42)(43)(44) to prevent loss due to cyclization (45). Thus, the ProB-␥-glutamyl phosphate complex competes with N-acetyl glutamyl phosphate for the active site of ProA*.…”

Section: Discussionmentioning

confidence: 99%

A Synonymous Mutation Upstream of the Gene Encoding a Weak-Link Enzyme Causes an Ultrasensitive Response in Growth Rate

et al. 2016

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When microbes are faced with an environmental challenge or opportunity, preexisting enzymes with promiscuous secondary activities can be recruited to provide newly important functions. Mutations that increase the efficiency of a new activity often compromise the original activity, resulting in an inefficient bifunctional enzyme. We have investigated the mechanisms by which growth of Escherichia coli can be improved when fitness is limited by such an enzyme, E383A ProA (ProA*). ProA* can serve the functions of both ProA (required for synthesis of proline) and ArgC (required for synthesis of arginine), albeit poorly. We identified four genetic changes that improve the growth rate by up to 6.2-fold. Two point mutations in the promoter of the proBA* operon increase expression of the entire operon. Massive amplification of a genomic segment around the proBA* operon also increases expression of the entire operon. Finally, a synonymous point mutation in the coding region of proB creates a new promoter for proA*. This synonymous mutation increases the level of ProA* by 2-fold but increases the growth rate by 5-fold, an ultrasensitive response likely arising from competition between two substrates for the active site of the inefficient bifunctional ProA*. IMPORTANCEThe high-impact synonymous mutation we discovered in proB is remarkable for two reasons. First, most polar effects documented in the literature are detrimental. This finding demonstrates that polar effect mutations can have strongly beneficial effects, especially when an organism is facing a difficult environmental challenge for which it is poorly adapted. Furthermore, the consequence of the synonymous mutation in proB is a 2-fold increase in the level of ProA* but a disproportionately large 5.1-fold increase in growth rate. While ultrasensitive responses are often found in signaling networks and genetic circuits, an ultrasensitive response to an adaptive mutation has not been previously reported. Metabolic enzymes, although prodigious catalysts, are not perfectly specific for their physiological substrates. They typically possess secondary activities as a consequence of the assemblage of highly reactive functional groups, metal ions, and cofactors in their active sites. Secondary activities that are physiologically irrelevant, either because they are too inefficient to contribute to fitness or because the enzyme never encounters the substrate, are termed promiscuous activities (1).Promiscuous activities are important from an evolutionary standpoint because they provide a reservoir of catalytic potential within a proteome that can be drawn upon when the environment changes. A promiscuous activity may become important for fitness when a new source of carbon, nitrogen, or phosphorous appears in the environment or when a previously available compound, such as an amino acid or cofactor, becomes unavailable. A promiscuous activity may also become critical when the organism is exposed to a novel toxin, such as an antibiotic or pesticide.A newly recruited pro...

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“…The PcpB:PcpD system is not the first case in which kinetic evidence for a protein-protein interaction is compelling, but a physical interaction cannot be detected. Other examples include aspartyl kinase: aspartate semialdehyde dehydrogenase (34), glutamyl kinase: glutamate semialdehyde dehydrogenase (35), and glutamine phosphoribosylpyrophosphate amidotransferase:glycinamide ribonucleotide synthetase (26). The hypothesis that a proteinprotein interaction between PcpD and PcpB is responsible for the sequestration of TCBQ is supported by experiments showing that TCBQ is released to the solvent when PcpD-FeS is present, even though this truncated enzyme is kinetically competent for reduction of TCBQ.…”

Section: Discussionmentioning

confidence: 73%

“…Passage of an intermediate directly from one active site to another without equilibration with the solvent is called channeling (26)(27)(28)(29)(30). Examples of reactive intermediates that are channeled from one active site to another include carbamate (31), ammonia (32), indole (33), aspartyl phosphate (34), glutamyl phosphate (35), and phosphoribosylamine (26). TCBQ is even more reactive than these intermediates, undergoing reaction with thiols at physiologically relevant concentrations in milliseconds.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Sequestration of a highly reactive intermediate in an evolving pathway for degradation of pentachlorophenol

Yadid

Rudolph

Hlouchová

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Microbes in contaminated environments often evolve new metabolic pathways for detoxification or degradation of pollutants. In some cases, intermediates in newly evolved pathways are more toxic than the initial compound. The initial step in the degradation of pentachlorophenol by Sphingobium chlorophenolicum generates a particularly reactive intermediate; tetrachlorobenzoquinone (TCBQ) is a potent alkylating agent that reacts with cellular thiols at a diffusion-controlled rate. TCBQ reductase (PcpD), an FMN-and NADH-dependent reductase, catalyzes the reduction of TCBQ to tetrachlorohydroquinone. In the presence of PcpD, TCBQ formed by pentachlorophenol hydroxylase (PcpB) is sequestered until it is reduced to the less toxic tetrachlorohydroquinone, protecting the bacterium from the toxic effects of TCBQ and maintaining flux through the pathway. The toxicity of TCBQ may have exerted selective pressure to maintain slow turnover of PcpB (0.02 s −1 ) so that a transient interaction between PcpB and PcpD can occur before TCBQ is released from the active site of PcpB.biodegradation | molecular evolution | channeling | quinone reductase

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Substrate channeling in proline metabolism

Cited by 55 publications

References 70 publications

Proline Mechanisms of Stress Survival

Proline Mechanisms of Stress Survival

A Synonymous Mutation Upstream of the Gene Encoding a Weak-Link Enzyme Causes an Ultrasensitive Response in Growth Rate

Sequestration of a highly reactive intermediate in an evolving pathway for degradation of pentachlorophenol

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