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E Küster

Publications and source records attributed to E Küster.

At least 19 recordsLinked to original sources
PubMed2000

Dopamine D(3) receptors in the rat kidney: role in physiology and pathophysiology.

It is well accepted that dopamine receptors play an important role in the regulation of cardiovascular and kidney function. Most of the knowledge on the renal actions of dopamine has been accumulated focussing on the prototypes of the two known dopamine receptor subfamilies, i.e. D1 and D2. The dopamine D3 receptor is a member of the D2-like subfamily and has been intensively studied in the neurosciences. Recently, the peripheral actions of this receptor subtype have also raised considerable interest as well because its effects on kidney function appear to be different from that of the other dopamine receptors. This short overview will summarize the data reported and add new results on the role of D3 receptors in the regulation of renal function as well as their potential pathophysiological implications.

Animals↗
PubMed1998

Dopamine D3 receptor activation modulates renal function in anesthetized rats.

The renal effects of the D3 receptor agonist R(+)-7-hydroxy-dipropyl-aminotetraline (7-OH-DPAT) were studied in anesthetized Sprague-Dawley rats using standard clearance experiments. 7-OH-DPAT infusion (0.01, 0.1, and 1.0 microg kg(-1) min(-1)) dose-dependently increased glomerular filtration rate (GFR) compared to baseline by a maximum of 20+/-2% while arterial blood pressure was not affected. Heart rate was not altered during the two lower doses of 7-OH-DPAT whereas a slight reduction occurred due to infusion of 1.0 microg kg(-1) min(-1). In contrast, higher doses of 7-OH-DPAT, starting from 3 microg kg(-1) min(-1), markedly influenced systemic hemodynamics. In addition to the hyperfiltration, 7-OH-DPAT (1.0 microg kg(-1) min(-1)) also induced a significant diuresis (27.7+/-4.3 microl min(-1) 100 g(-1) vs 16.2+/-5.4 microl min(-1) 100 g(-1)) and increased both absolute (3.30+/-0.58 micromol min(-1) 100 g(-1) vs 0.95+/-0.26 micromol min(-1) 100 g(-1)) and fractional sodium excretion (2.48+/-0.32% vs 0.79+/-0.19%). These changes in renal function were not modulated by pretreatment with the D2 receptor antagonist S(-)-sulpiride but abolished by the D3 antagonist 5,6-dimethoxy-2-(di-n-propylamino)indane (U-99194A). In coincidence with the action of 7-OH-DPAT on both glomerular and tubular function, reverse transcription-polymerase chain reaction (RT-PCR) revealed the expression of D3 receptors in both glomerular and tubular fractions of kidneys taken from Sprague-Dawley rats. These data indicate that D3 receptors in the kidney are involved in the regulation of renal hemodynamics and tubular function.

Anesthesia↗
PubMed1998

Identification of a co-repressor binding site in catabolite control protein CcpA.

The catabolite control protein CcpA is the central regulator of carbon catabolite repression in Bacilli and other Gram-positive bacteria. A comparison of 12 CcpA-like sequences with regulators from the LacI/GalR family defines a CcpA subfamily based on extensive similarities found among CcpAs and not in 32 other members of the family. These amino acids are clustered in three blocks in the CcpA sequence. Their interpretation, assuming a PurR-like fold, reveals that almost all of them are surface exposed and form a continuous patch on the N-terminal subdomain of the protein core extending into the DNA reading head. We introduced nine single amino acid exchanges in the subfamily specific residues of CcpA from Bacillus megaterium. Six mutants, namely CcpA47RS, 79AE, 89YE, 295YR, 299YE and 303RD, are inactive or severely impaired in catabolite repression, underlining their relevance for CcpA function. They are negatively transdominant over wild-type CcpA demonstrating their ability to correctly fold for dimerization. Five of them are unable or impaired in binding HPr-Ser-46-P in vitro, establishing a correlation between catabolite repression efficiency and HPr-Ser-46-P binding. These results support the hypothesis that the conserved region in CcpA is the HPr-Ser-46-P binding site.

Amino Acid Sequence↗
PubMed1998

Urinary dopamine and renal handling of L-DOPA in fasted spontaneously hypertensive rats.

A defective renal dopaminergic system has been suggested to contribute, via impaired sodium excretion, to the pathogenesis of hypertension. Data according renal dopamine (DA) release in hypertension, however, are inconsistent. In the present study, we compared urinary DA excretion (UDAV), plasma free DA (PDA), and renal tissue DA contents (TDA) of young spontaneously hypertensive rats (SHR), Wistar-Kyoto (WKY), and Sprague-Dawley (SD) rats. Since the protein intake dominantly controls UDAV, fasted animals were used to exclude the influence of feeding. Conscious WKY and SHR had a similar UDAV which was lower compared to SD rats. Thiopental anesthesia increased UDAV in SHR and WKY but not in SD rats. TDA was higher in SHR compared to SD and WKY rats. To investigate the tubular capacity to generate DA, the response to L-DOPA infusion was assessed in two doses. 1 nmol/min/100 g body weight L-DOPA increased UDAV approximately 30-fold in all strains but did not affect tubular sodium excretion or renal hemodynamics. In contrast, infusion of 3 micromol/min/100 g body weight L-DOPA increased UDAV by five orders of magnitude and induced natriuresis, diuresis, and tachycardia. These effects were assigned to an increase in PDA and no significant differences were observed among the strains. We conclude that, regarding renal DA, (1) the differences among SHR, WKY, and SD rats rather appear to be strain related than hypertension associated; (2) the renal capacity of DA generation from L-DOPA is not impaired in SHR; (3) tubular DA at physiological concentrations does not alter sodium excretion significantly in normo- or hypertensive rats, and (4) the influence of anesthesia on UDAV should be considered in comparative studies.

Animals↗
PubMed1997

Binding of the catabolite repressor protein CcpA to its DNA target is regulated by phosphorylation of its corepressor HPr.

Catabolite repression of a number of catabolic operons in bacilli is mediated by the catabolite control protein CcpA, the phosphocarrier protein HPr from the phosphoenolpyruvate-dependent sugar transport system (PTS), and a cis-acting DNA sequence termed the catabolite-responsive element (cre). We present evidence that CcpA interacts with HPr that is phosphorylated at Ser46 (Ser(P) HPr) and that these proteins form a specific ternary complex with cre DNA. Titration experiments following the circular dichroism signal of the cre DNA indicate that this complex consists of two molecules of Ser(P) HPr, a CcpA dimer, and the cre sequence. Limited proteolysis experiments indicate that the domain structure of CcpA is similar to other members of the LacI/GalR family of helix-turn-helix proteins, comprised of a helix-turn-helix DNA domain and a C-terminal effector domain. NMR titration of Ser(P) HPr demonstrates that the isolated C-terminal domain of CcpA forms a specific complex with Ser(P) HPr but not with unphosphorylated HPr. Based upon perturbations to the NMR spectrum, we propose that the binding site of the C-terminal domain of CcpA on Ser(P) HPr forms a contiguous surface that encompasses both Ser(P)46 and His15, the site of phosphorylation by enzyme I of the PTS. This allows CcpA to recognize the phosphorylation state of HPr, effectively linking the process of sugar import via the PTS to catabolite repression in bacilli.

Bacterial Proteins↗
PubMed1997

Cooperative and non-cooperative DNA binding modes of catabolite control protein CcpA from Bacillus megaterium result from sensing two different signals.

Carbon catabolite repression (CCR) of several operons in Bacillus subtilis and Bacillus megaterium is mediated by the cis-acting cre sequence and trans-acting catabolite control protein (CcpA). We describe purification of CcpA from B. megaterium and its interaction with regulatory sequences from the xyl operon. Specific interaction of CcpA with cre as scored by DNase I footprints at concentrations similar to the in vivo situation requires the presence of effectors. We have found two molecular effectors for CcpA activity, which lead to different recognition modes of DNA. The heat-stable phosphotransfer protein HPr from the PTS sugar uptake system triggers non-cooperative binding of CcpA to cre when phosphorylated at Ser46 (HPr-Ser46-P). Glucose 6-phosphate (Glc-6-P) triggers cooperative binding of CcpA to cre and two auxiliary cre* sites, one of which overlaps the -35 box of the xyl promoter. Binding to cre* depends on the presence of the functional cre sequence. A mutation in cre abolishes carbon catabolite repression in vivo and binding of CcpA to cre and cre* in vitro, indicating looping of the intervening DNA. The two triggers are not simultaneously active. The acidity of the buffer determines which of them activates CcpA when both are present in vitro. Glc-6-P is preferred at pH values below 5.4, and HPr-Ser46-P is preferred at neutral pH. The Ccpa dimers present at neutral pH form tetramers and higher oligomers at pH 4.6, explaining cooperativity of binding to DNA. CcpA is the first member of the LacI/GalR family of regulators, for which oligomerization without the leucine zipper at the C terminus is demonstrated.

Bacillus megaterium↗
PubMed1997

Regulation of expression, genetic organization and substrate specificity of xylose uptake in Bacillus megaterium.

Xylose uptake in Bacillus megaterium depends on expression of a putative H+/xylose symporter encoded by xylT, the last gene in the xyl operon. Insertional inactivation of xylT leads to an apparent uptake deficiency determined with whole cells and severely slower growth on xylose as sole carbon source. Expression of xylT is xylose inducible and subject to carbon catabolite repression mediated by CcpA and cre. Northern analysis of the xyl mRNA reveals that a potential stem-loop structure located in the non-translated region between xylA and xylB presumably acts as a transcriptional terminator, as it leads to different amounts of the respective mRNA sections: the 5'-xylA portion is very abundant, while the 3'-xylBT portion constitutes only a fraction of it. XylT has an apparent Michaelis constant (KM) of approx. 100 microM and is competitively inhibited by glucose with an inhibitor constant KI of 16 mM.

Aldose-Ketose Isomerases↗
PubMed1996

Immunological crossreactivity to the catabolite control protein CcpA Bacillus megaterium is found in many gram-positive bacteria.

The catabolite control protein CcpA from Bacillus megaterium was overproduced as a fusion protein to a 6xhis affinity tag and purified to homogeneity. Polyclonal antibodies of high affinity and specificity were raised against the purified protein. The serum did not crossreact with purified Lac repressor despite the fact that CcpA and LacI belong to the same protein family. Using this antiserum we identified proteins that share antigenic determinants with CcpA in many Gram-positive bacteria, including bacilli, staphylococci, lactic acid bacteria, and some actinomycetes.

Amino Acid Sequence↗
PubMed1996

Catabolite repression resistance of gnt operon expression in Bacillus subtilis conferred by mutation of His-15, the site of phosphoenolpyruvate-dependent phosphorylation of the phosphocarrier protein HPr.

Carbon catabolite repression of the gnt operon of Bacillus subtilis is mediated by the catabolite control protein CcpA and by HPr, a phosphocarrier protein of the phosphotransferase system. ATP-dependent phosphorylation of HPr at Ser-46 is required for carbon catabolite repression as ptsH1 mutants in which Ser-46 of HPr is replaced with an unphosphorylatable alanyl residue are resistant to carbon catabolite repression. We here demonstrate that mutation of His-15 of HPr, the site of phosphoenolpyruvate-dependent phosphorylation, also prevents carbon catabolite repression of the gnt operon. A strain which expressed two mutant HPrs (one in which Ser-46 is replaced by Ala [S46A HPr] and one in which His-15 is replaced by Ala [H15A HPr]) on the chromosome was barely sensitive to carbon catabolite repression, although the H15A mutant HPr can be phosphorylated at Ser-46 by the ATP-dependent HPr kinase in vitro and in vivo. The S46D mutant HPr which structurally resembles seryl-phosphorylated HPr has a repressive effect on gnt expression even in the absence of a repressing sugar. By contrast, the doubly mutated H15E,S46D HPr, which resembles the doubly phosphorylated HPr because of the negative charges introduced by the mutations at both phosphorylation sites, had no such effect. In vitro assays substantiated these findings and demonstrated that in contrast to the wild-type seryl-phosphorylated HPr and the S46D mutant HPr, seryl-phosphorylated H15A mutant HPr and H15E,S46D doubly mutated HPr did not interact with CcpA. These results suggest that His-15 of HPr is important for carbon catabolite repression and that either mutation or phosphorylation at His-15 can prevent carbon catabolite repression.

Bacillus subtilis↗
PubMed1995

In vitro binding of the CcpA protein of Bacillus megaterium to cis-acting catabolite responsive elements (CREs) of gram-positive bacteria.

Using DNA band migration retardation assays, specific binding of the CcpA protein of Bacillus megaterium to the cis-acting catabolite responsive element (CRE) of the xyl operon of B. subtilis has been demonstrated. Binding of CcpA was specifically inhibited by addition of unlabeled DNA fragments containing CREs of other operons but not by DNA fragments lacking a CRE. Binding was stimulated by high concentrations of phosphate, pyrophosphate, and organic phosphate esters and specifically inhibited by serine phosphorylated HPr and its conformational analogue, S46D HPr. This report therefore documents the specific binding of CcpA to a target CRE and defines its regulation by HPr(ser-P) and phosphorylated metabolites.

Bacillus megaterium↗
PubMed1995

Protein kinase-dependent HPr/CcpA interaction links glycolytic activity to carbon catabolite repression in gram-positive bacteria.

CcpA, the repressor/activator mediating carbon catabolite repression and glucose activation in many Gram-positive bacteria, has been purified from Bacillus megaterium after fusing it to a His tag. CcpA-his immobilized on a Ni-NTA resin specifically interacted with HPr phosphorylated at seryl residue 46. HPr, a phospho-carrier protein of the phosphoenolpyruvate: glycose phosphotransferase system (PTS), can be phosphorylated at two different sites: (i) at His-15 in a PEP-dependent reaction catalysed by enzyme I of the PTS; and (ii) at Ser-46 in an ATP-dependent reaction catalysed by a metabolite-activated protein kinase. Neither unphosphorylated HPr nor HPr phosphorylated at His-15 nor the doubly phosphorylated HPr bound to CcpA. The interaction with seryl-phosphorylated HPr required the presence of fructose 1,6-bisphosphate. These findings suggest that carbon catabolite repression in Gram-positive bacteria is a protein kinase-triggered mechanism. Glycolytic intermediates, stimulating the corresponding protein kinase and the P-ser-HPr/CcpA complex formation, provide a link between glycolytic activity and carbon catabolite repression. The sensitivity of this complex formation to phosphorylation of HPr at His-15 also suggests a link between carbon catabolite repression and PTS transport activity.

Amino Acid Sequence↗
PubMed1983

Influence of different dietary regimens upon the composition of the human fecal flora.

The composition of the fecal flora in two groups of children in primary school age with (a) normal, ad libitum diet (school-group, 20 children), and (b) lacto-ovo-vegetarian diet (Salem-group, 20 children) was examined. Fecal analysis was concentrated upon the isolation of the main anaerobic and aerobic microorganisms. The pattern of S-, M-, and R-forms of Enterobacteriaceae with special regard to E. coli was investigated additionally. In the school-group counts of Clostridium species, R-, and M- forms of E. coli were significantly higher than in the Salem-group. The numbers of Bifidobacterium, Actinomyces, and Enterobacteriaceae species, as well as S-forms of E. coli were significantly increased in the Salem-group, as compared to the school-children. The data reveal a relationship between the occurrence of different anaerobic species and the SMR-pattern of E. coli, with Clostridium species in particular. The SMR-pattern of E. coli may reflect conditions of intestinal metabolism and mucosal immunity. It may serve as a simple parameter in routine examination of fecal specimen.

Bacteria↗
PubMed1982

Formation of fertile aerial mycelium within asporogenous streptomycetes as induced by fungal metabolites.

Asporogenous streptomycetes, e. g. Streptomyces flavochromogenes and S. luteolutescens, become able to form fertile aerial mycelium when they are cultivated in close contact with fungi. This may be caused by the production and secretion of fungal metabolites which induce or stimulate the aerial mycelium formation. An attempt was made to characterize the stimulatory factor. Among the numerous fungi tested the most active ones were Cladosporium cladosporioides and Drechslera erythrospila.

Amino Acids↗
PubMed1978

[Studies on the composting of feathers (author's transl)].

The nitrogen of keratin of feathers is not taken up by plants as a suitable N-source. It becomes available by the keratinolytic activity of microorganisms. The high temperature evolved during the composting process promotes the growth and activity of thermophilic, keratin-decomposing microorganisms, e.g. Thermoactinomyces vulgaris. The increasing in temperature (self-heating) reflects the course of composting. A feather-peat mixture exhibits a considerably high heat production, i.e. a fast decomposition of keratin and other organic matter.

Agriculture↗