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A Bax

Publications and source records attributed to A Bax.

At least 127 records · Page 7Linked to original sources
PubMed1988

Long-range 15N-1H correlation as an aid to sequential proton resonance assignment of proteins. Application to the DNA-binding protein ner from phage Mu.

A method is described for sequential resonance assignment of protein 1H-NMR spectra relying on the detection of long-range correlations between 15N and C alpha H atoms using 1H-detected heteronuclear multiple-bond correlation spectroscopy. In particular, the observation of the two-bond 15N(i)-C alpha H(i) and three-bond 15N(i)-C alpha H(i-1) correlations enables one to connect one residue with the next. Because the magnitude of the long-range couplings is small (less than 6 Hz), the sensitivity of this experiment is necessarily low and requires the use of 15N-enriched protein samples. Further, because the size of the 15N(i)-C alpha H(i-1) coupling is very sensitive to the psi backbone torsion angle, structural information can be derived. The application of this experiment is illustrated with the 75-residue DNA-binding protein ner from phage Mu.

Coliphages↗
PubMed1988

NMR signal assignments of amide protons in the alpha-helical domains of staphylococcal nuclease.

We report complete assignments of the amide proton signals in the three long dNN connectivity sequences observed in the NOESY spectrum of deuteriated staphylococcal nuclease (Nase) complexed with thymidine 3',5'-bisphosphate (pdTp) and Ca2+, Mr 18K. The assignments are made by comparing NOESY spectra with 1H-15N and 1H-13C heteronuclear multiple-quantum shift correlation (HMQC) spectra of Nase samples containing 15N- and 13C-labeled amino acids. The assignments show that the residues which are linked by the dNN connectivity sequences are located in three alpha-helical domains of Nase. Our results indicate that by combining NOESY and HMQC spectra of appropriately labeled samples it should be possible to delineate and study alpha-helical domains in soluble proteins having molecular weights that are greater than 18K.

Amides↗
PubMed1988

Structural studies of the Escherichia coli K93 and K53 capsular polysaccharides.

The structures of the Escherichia coli K93 and K53 capsular polysaccharides have been investigated by chemical and spectroscopic methods. The repeating unit of both polymers was found to be----3)-beta-D-Galf-(1----f)-beta-D-GlcAp-(1. The O-5 and O-6 atoms of D-galactose are acetylated in the repeating unit of the K93 polymer, but only O-2 is acetylated in the K53 polymer. The K93 polysaccharide is cross-reactive with the Neisseria meningitidis Group A capsular polysaccharide (of known structure). The K53 polysaccharide, although structurally similar to that from K93 organisms, does not cross-react with the Group A polymer.

Carbohydrate Conformation↗
PubMed1988

A two-dimensional NMR study of the antimicrobial peptide magainin 2.

Using two-dimensional NMR spectroscopy, a complete 1H resonance assignment has been obtained for the peptide magainin 2 recently isolated from Xenopus laevis. It is demonstrated that this peptide adopts an alpha-helical structure with amphiphilic character when dissolved in a mixture of trifluoroethanol (TFE) and H2O. The transition to the alpha-helical conformation occurs at very low concentrations of TFE.

Animals↗
PubMed1987

Application of new, high-sensitivity, 1H-13C-n.m.r.-spectral techniques to the study of oligosaccharides.

Four n.m.r. methods that are especially useful for characterization of oligosaccharides are applied to the trisaccharide alpha-Neu5Ac-(2----3)-beta-Gal-(1----4)-Glc (1). Three of these are two-dimensional, heteronuclear methods that provide chemical-shift correlation maps having much higher sensitivity than was previously possible, because they rely on indirect observation of 13C via 1H detection. These methods are used to assign, completely, the 1H- and 13C-n.m.r. spectra of both anomers of the trisaccharide. In addition to these two-dimensional methods, a one-dimensional method is used to measure 1H-1H coupling-constants accurately within each sugar ring. The values of the coupling constants thus measured for 1 are evidence that the conformations of the individual sugar rings are not affected by linkage into the trisaccharide.

Carbohydrate Sequence↗
PubMed1987

New n.m.r.-spectroscopic approaches for structural studies of polysaccharides: application to the Haemophilus influenzae type a capsular polysaccharide.

The extension of several modern nuclear magnetic resonance (n.m.r.) spectroscopic techniques to polysaccharides is discussed and illustrated, using the native Haemophilus influenzae type a capsular polysaccharide. These techniques provide for the unambiguous assignment of all n.m.r. resonances (1H, 13C, and 31P) via high-sensitivity homonuclear and 1H-detected heteronuclear correlations, and they are capable of locating the intersaccharide linkages (both O-linked and phosphoric diester-linked) and appended groups (e.g. O-acetyl groups). To illustrate the power and sensitivity of these methods, a 10-mg sample of the H. Influenzae type a polysaccharide (repeat unit mol. wt. = 376) was studied. The combined acquisition time for the two-dimensional 1H-13C correlation data (one-bond and multiple-bond), the 1H-31P correlation data, and the 1H-1H (homonuclear Hartmann-Hahn) data was approximately 18 h.

Carbohydrate Conformation↗
PubMed1987

Absorption mode two-dimensional NOE spectroscopy of exchangeable protons in oligonucleotides.

A new NMR method is described for the generation of absorption mode two-dimensional NOE spectra of oligonucleotides in H2O solution. The method yields spectra that are free of baseline distortions with excellent suppression of the intense H2O resonance. The method is demonstrated for a sample of the dodecamer d(CGCGAATTCGCG)2. All exchangeable base protons are identified and a number of new types of NOE connectivities are observed.

Amines↗
PubMed1986

Assignment of the 31P and 1H resonances in oligonucleotides by two-dimensional NMR spectroscopy.

The use of new 1H-detected heteronuclear 1H-31P shift correlation experiments is demonstrated for oligonucleotides of 12 and 40 base pairs. The methods give unambiguous assignments of the 31P resonances and also permit identification of the C4' and C5' sugar protons. Use of the new methods enables one to make sequence-specific resonance assignments without reference to a known or assumed conformation of the DNA fragment.

DNA↗
PubMed1986

Two-dimensional nuclear magnetic resonance spectroscopy.

Great spectral simplification can be obtained by spreading the conventional one-dimensional nuclear magnetic resonance (NMR) spectrum in two independent frequency dimensions. This so-called two-dimensional NMR spectroscopy removes spectral overlap, facilitates spectral assignment, and provides a wealth of additional information. For example, conformational information related to interproton distances is available from resonance intensities in certain types of two-dimensional experiments. Another method generates 1H NMR spectra of a preselected fragment of the molecule, suppressing resonances from other regions and greatly simplifying spectral appearance. Two-dimensional NMR spectroscopy can also be applied to the study of 13C and 15N, not only providing valuable connectivity information but also improving sensitivity of 13C and 15N detection by up to two orders of magnitude.

Carbon↗
PubMed1985

Escherichia coli K51 and K93 capsular polysaccharides are crossreactive with the group A capsular polysaccharide of Neisseria meningitidis. Immunochemical, biological, and epidemiological studies.

Eleven Escherichia coli strains, crossreactive with the capsular polysaccharide (CPS) of Neisseria meningitidis group A (GrA), were detected among 645 stool isolates from healthy families in Cairo, Egypt. 10 of these strains were of the O107:K93:H27 or O107:K93:SP serotypes and may be considered descendents of a single bacterium or as a clone. The remaining crossreactive strain was of the O7:K51:H18 serotype. None of the 11 strains produced enterotoxins and none were enteroinvasive. The purified CPS of these E. coli strains, as well as a polysaccharide (PS) from B. pumilis, strain Sh17, precipitated with equine GrA (H49) antiserum. A partial identity between the E. coli K93, K51 and Sh17 PS on the one hand and the GrA CPS on the other was observed by double immunodiffusion when reacted against the H49 antiserum. Four K93 strains and one K51 strain were found among 320 E. coli strains from patients at the Clinical Center, National Institutes of Health, and three K93 strains were found in 105 stool samples from children in Copenhagen. The data from these three surveys suggest that these crossreactive E. coli are common organisms and could serve as a stimulus for "natural" GrA CPS antibodies. Quantitative precipitation analysis showed that K51, K93, and Sh17 PS precipitated 25, 46.8, and 50% of H49 antibodies, respectively. Absorption of H49 antiserum with the GrA CPS removed its precipitating activity with the E. coli K93, K51, and Sh17 PS. Absorption of H49 antiserum with either K51 CPS or Sh17 PS removed the homologous crossreactivity only, whereas K93 CPS absorbed both K93 and K51 reactivities. Antibodies, raised by intravenous injection of formalinized E. coli K93 or K51 cells into rabbits, precipitated with GrA CPS and were bactericidal against GrA meningococci. The crossreaction between the E. coli K93 and the GrA CPS was unexpected since these two CPS are compositionally so dissimilar.

Absorption↗
PubMed1985

15N-labeled Escherichia coli tRNAfMet, tRNAGlu, tRNATyr, and tRNAPhe. Double resonance and two-dimensional NMR of N1-labeled pseudouridine.

The N1 imino units in Escherichia coli tRNAfMet, tRNAGlu, tRNAPhe, and tRNATyr were studied by 1H-15N NMR using three different techniques to suppress signals of protons not attached to 15N. Two of the procedures, Fourier internuclear difference spectroscopy and two-dimensional forbidden echo spectroscopy permitted 1H and 15N chemical shifts to be measured simultaneously at 1H sensitivity. The tRNAs were labeled by fermentation of the uracil auxotroph S phi 187 on a minimal medium containing [1-15N]uracil. 1H and 15N resonances were detected for all of the N1 psi imino units except psi 13 at the end of the dihydrouridine stem in tRNAGlu. Chemical shifts for imino units in the tRNAs were compared with "intrinsic" values in model systems. The comparisons show that the A X psi pairs at the base of the anticodon stem in E. coli tRNAPhe and tRNATyr have psi in an anti conformation. The N1 protons of psi in other locations, including psi 32 in the anticodon loop of tRNAPhe, form internal hydrogen bonds to bridging water molecules or 2'-hydroxyl groups in nearby ribose units. These interactions permit psi to stabilize the tertiary structure of a tRNA beyond what is provided by the U it replaces.

Escherichia coli↗
PubMed1985

Physico-chemical and microbiological comparison of nystatin, amphotericin A and amphotericin B, and structure of amphotericin A.

Two polyene antibiotics, nystatin and amphotericin A, were compared by physico-chemical and microbiological methods. The two antibiotics were found to have the same molecular weight, 926, by plasma desorption and electron-impact MS. However, 13C NMR spectrometry and HPLC studies indicated that the two molecules are different. The 200 MHz NMR studies indicated a chemical environment of 24 carbons of amphotericin A identical with that of the carbons of amphotericin B and nystatin. The structure of amphotericin A is identical with that of amphotericin B, except that there is a single bond between carbons 28 and 29 instead of a double bond, as shown by two-dimensional NMR studies.

Amphotericin B↗
PubMed1983

Multiple quantum two-dimensional 1H--15N nuclear magnetic resonance spectroscopy: chemical shift correlation maps for exchangeable imino protons of Escherichia coli tRNAMetf in water.

A procedure based on multiple quantum two-dimensional nuclear magnetic resonance spectroscopy is described for generation of 1H--15N chemical shift correlation maps. The method is used to obtain 15N chemical shifts for the exchangeable imino protons in 1H--15N units of site-specifically labeled Escherichia coli tRNAMetf in water. The high sensitivity and excellent chemical shift dispersion of the multiple quantum two-dimensional technique make it ideally suited for studying protonated nitrogens by NMR.

Escherichia coli↗