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R J Boerner

Publications and source records attributed to R J Boerner.

At least 37 records · Page 2Linked to original sources
PubMed1995

Catalytic activity of the SH2 domain of human pp60c-src; evidence from NMR, mass spectrometry, site-directed mutagenesis and kinetic studies for an inherent phosphatase activity.

During solution structural studies it was apparent that the human recombinant pp60c-src SH2 domain (srcSH2, residues 144-249) possessed an inherent phosphatase (Pase) activity. Complexes of U[13C,15N]srcSH2 with unlabeled Ac-pYEEIE (I) were examined using 31P and 1H-detected isotope filtered NMR methods. The presence of a high-affinity complex in equimolar solutions of I and U[13C, 15N]-srcSH2 was demonstrated by chemical shift perturbations, line broadening, and the observation of intermolecular nuclear Overhauser effects from the pY and Ile side-chain protons of I to protons on amino acid residues present in the binding pocket of srcSH2. Solutions containing excess I relative to srcSH2 revealed a slow hydrolysis of I to produce Ac-YEEIE and inorganic phosphate. The hydrolysis rate determined from NMR and HPLC-electrospray ionization mass spectrometry data at 30 degrees C for solutions containing excess I was 0.002-0.003 h-1. srcSH2 also catalyzed the hydrolysis of p-nitrophenyl phosphate (pNPP). Isoelectric focusing gels of a number of mutant srcSH2s demonstrated that this activity comigrated with srcSH2. Km, kcat, and kcat/Km were 3.7 +/- 0.4 mM, 3.1 +/- 0.2 x 10(-2) min-1, and 8.4 +/- 0.4 M-1 min-1, respectively, toward pNPP. The C188A mutant of the srcSH2 domain displayed 15% of the activity displayed by wild-type srcSH2, demonstrating that this residue is not absolutely required for activity. Two additional mutations in the known pY binding site, R178K and R158K, also resulted in decreased pNPPase activity, suggesting that the activity resides in or near this site. The inhibitor profile and pH dependence suggest that this is a novel protein Pase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Examination of the dephosphorylation reactions catalyzed by pp60c-src tyrosine kinase explores the roles of autophosphorylation and SH2 ligand binding.

pp60c-src tyrosine kinase (srcTK) catalyzes the dephosphorylation of phosphotyrosine-containing peptides, including phosphopeptides that bind with high affinity to the src SH2 domain. The mechanism for these dephosphorylation reactions was investigated. Dephosphorylation was inhibited by a competitive inhibitor for the ATP binding site. In the presence of ADP, dephosphorylation of phosphopeptide substrates is primarily due to the reversal of the kinase reaction. Autoactivated and unactivated srcTK both catalyzed the reverse of the kinase reaction; however, autoactivated srcTK displayed an increase in kcat of approximately 4-11-fold relative to unactivated srcTK, depending on the reaction conditions. Autoactivation of srcTK does not affect the Km's for MgADP or phosphopeptide (FGE)3-pY-(GEF)2GD. Unphosphorylated srcTK becomes phosphorylated during the reverse of the kinase reaction upon accumulation of free MgATP. In the presence of MgATP, srcTK also dephosphorylates peptide substrates, by first hydrolyzing MgATP to MgADP. Binding of phosphotyrosine peptide ligands to the src SH2 domain stimulated the rate of MgATP hydrolysis approximately 2-fold, but had not effect on the Km for MgATP. These data suggest that autophosphorylation of tyrosine 419 is not required for nucleotide or peptide binding, or catalysis involving small peptide substrates. In addition, these results suggest that both the forward and the reverse src tyrosine kinase reactions may be important in regulating the intracellular levels of protein tyrosine phosphorylation.

Adenosine Diphosphate↗
PubMed1995

[Integrated treatment strategies in panic disorder with agoraphobia and depressive disorder].

Two patients suffering from a panic disorder (agoraphobia) as well as a depressive disorder and alcohol abuse showed marked improvement when given a combination of pharmacotherapy and behavior therapy. The feasibility of this combination treatment in the context of understanding both the theory and therapy of panic disturbances is discussed in these two case histories.

Adult↗
PubMed1995

[Treatment refractory panic disorder--success of a combined treatment with imipramine, moclobemide and behavior therapy].

The subject of how to treat patients suffering from severe panic attacks and concomitant symptoms has in the past been insufficiently discussed although these patients typify a legitimate clinical group. This case report deals with a patient with a long history of panic disturbances including agoraphobia, social phobia, depressive moods and alcohol abuse, whose condition remitted only after applying a supplementary treatment, using Imipramine and Moclobimide in conjunction with behavioural therapy. Criteria of panic disturbances not yielding to treatment and potential therapeutic measures are being discussed.

Adult↗
PubMed1994

Comparison of cytochrome b-559 content in photosystem II complexes from spinach and Synechocystis species PCC 6803.

Cytochrome b-559 is an integral component of photosystem II complexes from both plants and cyanobacteria. However, the number of cytochrome b-559 associated with the photosystem II reaction center has been the subject of controversy. Some studies have concluded that there is one heme equivalent of cytochrome b-559 per reaction center, some studies have found two, and some studies have reported intermediate values. Most of the previous experiments have used only one method to quantitate the antenna size of the preparation. In this study, we compare the cytochrome b-559 content in a cyanobacterial and a plant photosystem II preparation. The plant preparation is derived from spinach, and previous work has shown that it has an antenna size of approximately 100 chlorophylls [MacDonald, G. M., & Barry, B. A. (1992) Biochemistry 31, 9848-9856]. The cyanobacterial preparation is from Synechocystis sp. PCC 6803, and previous work has shown that it has an antenna size of approximately 60 chlorophylls [Noren, G. H., Boerner, R. J., & Barry, B. A. (1991) Biochemistry 30, 3943-3950]. Both preparations are isolated through the use of ion-exchange chromatography, and both preparations are monodisperse in the same nonionic detergent. In our comparative study, we quantitate antenna size by three different methods. Our work shows that, depending on the method used to estimate antenna size, the oxygen-evolving spinach photosystem II preparation contains 0.82-1.0 cytochrome b-559 per reaction center, while the oxygen-evolving cyanobacterial preparation contains 1.5-2.1 cytochrome b-559 per reaction center.

Cyanobacteria↗
PubMed1994

EPR evidence that the M+ radical, which is observed in three site-directed mutants of photosystem II, is a tyrosine radical.

Isotopic labeling of Synechocystis sp. PCC 6803 and EPR spectroscopy have been used to demonstrate that photosystem II contains two redox active tyrosines, D and Z (Barry, B. A. and Babcock, G. T. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 7099-7103; Boerner, R. J. and Barry, B. A. (1993) J. Biol. Chem. 268, 17151-17154). Another organic radical, M+, has recently been observed in site-directed mutants in which a non-redox active amino acid is substituted at either the putative D or putative Z sites (Boerner, R. J., Bixby, K. A., Nguyen, A. P., Noren, G. H., Debus, R. J., and Barry, B. A. (1993) J. Biol. Chem. 268, 1817-1823; Noren, G. H., and Barry, B. A. (1992) Biochemistry 31, 3335-3342). Here, we use isotopic labeling to determine the chemical identity of M+. Upon incorporation of perdeuterated tyrosine into photosystem II, the M+ EPR signal narrows to approximately 12-13 G. Labeling with 3,5-deuterated tyrosine results in an isotropic doublet with splittings of 11 G. Our results show that M+ is a tyrosine radical with unique spectroscopic properties.

Cyanobacteria↗
PubMed1993

Isotopic labeling and EPR spectroscopy show that a tyrosine residue is the terminal electron donor, Z, in manganese-depleted photosystem II preparations.

Photosystem II contains two redox active species, D and Z, which in the oxidized and paramagnetic form give rise to similar EPR signals. Both signals are broadened by anisotropic interactions and show no well-resolved hyperfine splittings, even at room temperature. D+ is a dark stable radical of unknown function. Z, on the other hand, acts as the intermediate electron carrier between the primary chlorophyll donor and the manganese catalytic site. In manganese-depleted photosystem II preparations, where Z+ is the terminal electron donor, the Z+ EPR signal can be easily detected. Isotopic labeling of intact cells of Synechocystis 6803 and EPR spectroscopy were used to demonstrate that D+ is a tyrosine radical (Barry, B.A., and Babcock, G. T. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 7099-7103). However, since the Z+ signal is not observable in intact cyanobacterial cells, a definitive assignment of the Z redox active species has not yet been performed. Here, we describe the use of a purified photosystem II preparation to assign the Z+ EPR signal to a neutral tyrosine radical. Further, a comparison of the Z+ and D+ EPR lineshapes in deuterated samples shows that there are slight differences between the two signals. These alterations may be caused by differences in the protein environments of the D+ and Z+ radicals.

Cyanobacteria↗
PubMed1993

Removal of stable tyrosine radical D+ affects the structure or redox properties of tyrosine Z in manganese-depleted photosystem II particles from Synechocystis 6803.

Photosystem II contains two redox-active tyrosines, D and Z. To understand the function of the dark stable tyrosine radical, D+, we have characterized two site-directed mutations at the D tyrosine residue in the transformable cyanobacterium, Synechocystis sp. PCC 6803, through the use of purified photosystem II particles (Noren, G. H., Boerner, R. J., and Barry, B. A. (1991) Biochemistry 30, 3943-3950). In manganese-depleted mutant particles, a light-induced EPR signal is observed. This signal contains a stable component, due to a chlorophyll radical, and an unstable component. The lineshape of the unstable, oxidized component, which we call M+, is obtained by subtraction; it has a lineshape different from tyrosine Z+/D+ and a g value of 2.004. Up to one M+ spin per reaction center can be photooxidized. The characteristic light-induced EPR signal ascribed to Z+ is not detected; under the same conditions, Z+ is detected in control preparations. The M+ radical lineshape is similar to the light-induced photosystem II radical identified in a site-directed mutant in the D1 polypeptide (YF161D1) (Noren, G. H., and Barry, B. A. (1992) Biochemistry 31, 3335-3342). Optical measurements on manganese-depleted photosystem II particles from control and D2 mutant preparations show that charge recombination kinetics between Q-A and an oxidized redox-active component are similar, to within a factor of two, in all three preparations. We conclude that lack of the stable tyrosine D+ alters the structure or redox properties of tyrosine Z in manganese-depleted preparations.

Base Sequence↗
PubMed1992

Evidence from directed mutagenesis that aspartate 170 of the D1 polypeptide influences the assembly and/or stability of the manganese cluster in the photosynthetic water-splitting complex.

To identify amino acid residues that influence the assembly or stability of the manganese cluster in photosystem II, we have generated site-directed mutations in the D1 polypeptide of the cyanobacterium, Synechocystis sp. PCC 6803. Indirect evidence has suggested that the D1 polypeptide provides some of the ligands that are required for metal binding. Mutations at position 170 of D1 were selected for characterization, since an aspartate to asparagine mutation (DN170D1) at this position completely abolishes photoautotrophic growth, while retention of a carboxylic acid at this position (aspartate to glutamate, DE170D1) supports photoautotrophic growth. Photosystem II particles were purified from control, DE170D1, and DN170D1 cells by a procedure that retains high rates of oxygen evolution activity in control particles [Noren, G.H., Boerner, R.J., & Barry, B.A. (1991) Biochemistry 30, 3943-3950]. Spectroscopic analysis shows that the tyrosine radical, Z+, which normally oxidizes the manganese cluster, is rapidly reduced in the DE170D1 mutant, but not in the DN170D1 mutant. A possible explanation of this block or dramatic decrease in the rate of electron transfer between the manganese cluster and tyrosine Z is an alteration in the properties of the metal center. Quantitation of manganese in these particles is consistent with aspartate 170 influencing the stability or assembly of the manganese cluster, since the aspartate to asparagine mutation results in a decrease in the manganese content per reaction center. Photosystem II particles from DN170D1 show a 60% decrease in the amount of specifically bound manganese per reaction center, when compared to control particles. Also, we observe a 70% decrease in the amount of specifically bound manganese per reaction center in partially purified DN170D1 particles and at least an 80% decrease in the amount of hydroxylamine-reducible manganese in DN170D1 thylakoid membranes. Single-turnover fluorescence assays and steady-state EPR measurements demonstrate that the remaining, endogenous manganese does not rapidly reduce tyrosine Z+ in the DN170D1 mutant. Additional evidence that aspartate 170 influences the assembly or stability of the metal site comes from analysis of the DE170D1 mutant. Although this mutant assembles a functional manganese cluster, as assessed by oxygen evolution and spectroscopic assays, the properties of the manganese site are perturbed.

Amino Acid Sequence↗
PubMed1991

EPR characterization of an oxygen-evolving photosystem II preparation from the transformable cyanobacterium Synechocystis 6803.

The transformable cyanobacterium Synechocystis 6803 has a photosynthetic apparatus that is similar to that of plants. Because of the ease with which this organism can be genetically manipulated and isotopically labeled, Synechocystis has been used extensively in recent studies of electron transfer in the water-splitting complex, photosystem II. Here, we present the first EPR characterization of a highly active oxygen-evolving preparation from this organism. This preparation shows oxygen-evolution activities in the range from 2400-2600 mumol of O2/(mg of chlorophyll.h). We show that this preparation is stable enough for room temperature EPR studies. We then use this assay to show that the lineshapes of the D+ and Z+ tyrosine radicals are identical in this preparation, as has been observed in photosystem II complexes from a wide variety of photosynthetic species. We also present the first multiline EPR spectrum that has been observed from the Synechocystis manganese cluster.

Blotting, Western↗
PubMed1989

Enzymatic synthesis and inhibitory characteristics of tartronate semialdehyde phosphate.

The immediate product of the pyruvate kinase catalyzed phosphorylation of beta-hydroxypyruvate is the enol of tartronate semialdehyde phosphate (TSP). The reaction has the same pH profile as that for the phosphorylation of pyruvate with pK's of 8.2 and 9.7 observed in H2O. This enol tautomerizes in solution to the aldehyde, which in turn becomes hydrated. 31P NMR spectra indicate that the enol resonates approximately 1 ppm upfield from the hydrated aldehyde. By following the tautomerization spectrophotometrically at 240 nm, we have found it to be independent of pH (0.2 min-1 below pH 6 in water), except that it is 2-fold slower above the pK of the phosphate group (6.3 in H2O and 6.7 in D2O). It is 3.6-fold slower in D2O. When this TSP is reduced with NaBH4, approximately 50% of the product is D-2-phosphoglyceric acid (substrate for enolase). Thus, while the immediate product of the phosphorylation rection is the enol of TSP, the eventual product is D,L-TSP. Both the enol and the aldehyde forms of TSP were found to be potent inhibitors of yeast enolase with apparent Ki values of 100 nM and 5 microM, respectively. However, since the aldehyde form is 95-99% hydrated [Stubbe, J., & Abeles, R. (1980) Biochemistry 19, 5505], the true Ki for the aldehyde species is 50-250 nM. The enol of TSP shows slow binding behavior, as expected for an intermediate analogue, with a t1/2 for this process of approximately 15 s (k = 0.046 s-1) and an initial Ki of approximately 200 nM.

Cadmium↗
PubMed1984

Curriculum evaluation, education financing, and career plans of 1983 medical school graduates.

The Association of American Medical Colleges annually gathers data on curriculum evaluation, financing, and career plans from senior medical students through a graduation questionnaire. According to the 1983 survey, a majority of the seniors perceived that an appropriate amount of time was devoted to the various areas of instruction at their institutions. The average indebtedness of the graduates was reported to be increasing, and 84.4 percent reported having medical school debts. Only 13.2 percent of the graduates indicated plans to enter a career in research, although over one-third had some research involvement while in medical school. Those who participated in research activities during medical school were somewhat more likely to plan significant research involvement after graduation than those who were not involved in research in medical school.

Career Choice↗