Regulatory adenylnucleotide-mediated binding of the PII-like protein SbtB to the cyanobacterial bicarbonate transporter SbtA is controlled by the cellular energy state

ABSTRACTCyanobacteria have evolved one of the most powerful CO2 concentrating mechanisms (CCM), supporting high photosynthetic rates with limiting inorganic carbon (Ci), which makes their CCM a desirable system for integration into higher plant chloroplasts to enhance photosynthetic yield. The CCM is driven by active Ci uptake, facilitated by bicarbonate transporters and CO2 pumps, which locally elevates the CO2 concentration and carboxylation rate of the primary CO2 fixing enzyme, Rubisco, inside cytoplasmic micro-compartments (carboxysomes). Ci uptake responds allosterically to Ci supply and light, but the molecular signals and regulators of protein function are unknowns. Functional analyses of sodium-dependent bicarbonate transporters classified as SbtA in E. coli support the hypothesis that SbtA activity is negatively regulated through association with its cognate PII-like SbtB protein. Here, we demonstrate that the association of SbtA with SbtB from two phylogenetically distant species, Cyanobium sp. PCC7001 and Synechococcus elongatus PCC7942, depends on the relative amounts of ATP or cAMP compared to ADP or AMP. Higher ATP over ADP or AMP ratios decreased the formation of SbtA:SbtB complexes, consistent with a sensory response to the cellular adenylate energy charge (AEC=[ATP + 0.5 ADP]/[ATP+ADP+AMP]) and the different binding affinities of these adenylates to SbtB protein trimers. Based on evidence for adenylate ligand-specific conformation changes for the SbtB protein trimer of Cyanobium sp. PCC7001, we propose a role for SbtB as a curfew protein locking SbtA into an inactive state as safe-guard against energetically futile and physiologically disadvantageous activation during prolonged low cellular AEC and photosynthetically unfavourable conditions.

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Regulation of Extra- and Intracellular pH in the Brain in Severe Hypoglycemia

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/jcbfm.1981.9 ◽

1981 ◽

Vol 1 (1) ◽

pp. 85-96 ◽

Cited By ~ 40

Author(s):

Dale Pelligrino ◽

Bo K. Siesjö

Keyword(s):

Intracellular Ph ◽

Ph Regulation ◽

Cell Damage ◽

Energy State ◽

Energy Charge ◽

Severe Hypoglycemia ◽

Cell Membrane Permeability ◽

Adenylate Energy Charge ◽

Acid Base ◽

The Brain

Severe hypoglycemia is associated with a marked curtailment of cerebral glucose supply and with consumption of endogenous carbohydrate metabolites and amino acids, many of which exist as anions of acids. Since metabolic control of intracellular pH in acute hypo- and hypercapnia seems to be dependent on the production and consumption of metabolic acids, it must be suspected that intracellular pH in the brain is poorly regulated in hypoglycemic animals. We induced hypocapnia (Paco2 about 15 mm Hg) and hypercapnia (Paco2 about 90 mm Hg) in insulin-injected animals in “precoma” (EEG pattern of slow waves, polyspikes) and “coma” (cessation of EEG activity) and measured CSF and intracellular acid-base changes using the CO2 method. The induced hypoglycemia did not measurably alter CSF acid-base changes from the normal during hypercapnia, but it did impair CSF pH regulation in hypocapnia. Animals in precoma showed an unchanged cerebral energy state during both hypo- and hypercapnia. Regulation of intracellular pH was not measurably affected in hypercapnia but was reduced in hypocapnia. These results could be accounted for by a reduced ability of the hypoglycemic animals to produce metabolic acids in response to the decrease in Pco2, while the capacity to “consume” acids was largely retained. In comatose animals, cerebral energy state was held at normocapnic levels during hypercapnia but deteriorated during hypocapnia. In the latter condition, the reduction in adenylate energy charge correlated to a decrease in blood pressure. The capacity to alter metabolic acid levels was abolished. In spite of this, hypocapnia was associated with a marked rise in intracellular pH, in some animals to values of about 7.7 (control, 7.0), and hypercapnia caused only very moderate reduction in intracellular pH. It is proposed that the excessive increase in intracellular pH during hypocapnia was due to hypotension-induced energy failure with subsequent depolarization of cells and passive equilibration of HCO3− (or H+) across the cell membranes. In hypercapnia, the influx of HCO3− into cells was unrelated to further deterioration of cerebral energy state but could possibly have been caused by CO2-induced depolarization and/or increased cell membrane permeability to HCO3−/H+ ions. It is concluded that severe hypoglycemia disrupts intracellular pH regulation in the brain and that hypocapnia combined with moderate hypotension leads to an excessive intracellular alkalosis of potential importance for the development of cell damage.

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The effect of new non-cross resistant antitumour agents on the energy state of human erythrocytes.

Acta Biochimica Polonica ◽

10.18388/abp.2005_3414 ◽

2005 ◽

Vol 52 (4) ◽

pp. 953-958

Author(s):

Robert Nowak ◽

Irena Baranowska-Bosiacka ◽

Barbara Stefańska ◽

Bogusław Machaliński ◽

Alina J Hłyńczak ◽

...

Keyword(s):

Promising Result ◽

Energy State ◽

Energy Charge ◽

Hplc Method ◽

Tumour Cells ◽

Human Erythrocytes ◽

Adenylate Energy Charge ◽

Active Efflux ◽

Antitumour Agents ◽

Energetic State

Multidrug resistance (MDR) of tumour cells is related to the overexpression of ATP-dependent pumps responsible for the active efflux of antitumour agents out of resistant cells. Benzoperimidine and anthrapyridone compounds exhibit comparable cytotoxic activity against sensitive and MDR tumour cells. They diffuse extremely rapidly across the plasma membrane and render the ATP-dependent efflux inefficient. Such uptake could disturb an energy metabolism of normal cells possessing an elevated level of ATP-dependent proteins, especially erythrocytes having a high level of the MRP1, MRP4 and MRP5 proteins. In this study the effect of five antitumour agents: benzoperimidine (BP1), anthrapyridones (CO1, CO7) and reference drugs used in the clinic: doxorubicin (DOX) and pirarubicin (PIRA), on the energetic state in human erythrocytes has been examined. These compounds have various types of structure and kinetics of cellular uptake (slow--DOX, CO7, moderate--PIRA, fast--BP1, CO1) resulting in their different ability to saturate ATP-dependent transporters. The energetic state of erythrocytes was examined by determination of purine nucleotide contents (ATP, ADP, AMP), NAD(+) and values of adenylate energy charge (AEC) using an HPLC method. It was found that the level of nucleotides as well as the AEC value of erythrocytes were not changed during 24 h of incubation with these agents independently of their structure and ability to saturate ATP-dependent pumps. This is a very promising result in view of their potential use in the clinic as antitumour drugs against multidrug resistant cancers.

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