Biomedical subjects

Q Teng

Publications and source records attributed to Q Teng.

24 records · Page 2Linked to original sources

PubMed1994

Solution 1H NMR determination of secondary structure for the three-iron form of ferredoxin from the hyperthermophilic archaeon Pyrococcus furiosus.

Two-dimensional 1H NMR data have been used to make sequence-specific assignments and define the secondary structure of the three-iron form of the oxidized ferredoxin, Fd, from the hyperthermophilic archaeon Pyrococcus furiosus, Pf. Signals for at least some protons were located for 65 of the 66 amino acids in the sequence, in spite of the paramagnetic (S = 1/2) ground state, but not all could be assigned. Unassigned and missing signals could be qualitatively correlated with the expected proximity of the protons to the paramagnetic cluster. The secondary structure was deduced from qualitative analysis of the 2D nuclear Overhauser effect, which identified two antiparallel beta-sheets, one triple-stranded including Ala1-Ser5, Val39-Glu41, and Thr62-Ala66, and one double-stranded consisting of Glu26-Asn28 and Lys32-Glu34, as well as an alpha-helix involving Glu43-Glu54. Three tight type I turns are located at residues Asp7-Thr10, Pro22-Phe25, and Asp29-Gly31. Comparison with the crystal structure of Desulfovibrio gigas, Dg, Fd (Kissinger et al., 1991) reveals a very similar folding topology, although several secondary structural elements are extended in Pf relative to Dg Fd. Thus the beta-sheet involving the two termini is expanded to include the two terminal residues and incorporates a third strand from the internal loop that is lengthened by several insertions in Pf relative to Dg Fd. The double-stranded beta-sheet in the interior of Pf Fd is lengthened slightly due to a much tighter type I turn between the two strands. The helix near the C-terminus is three residues longer in Pf than in Dg Fd, as well as being shifted toward the N-terminus. The disulfide link between the two nonligating Cys residues (Cys21 and Cys48) is conserved in Pf Fd, but the link near the C-terminus is in the middle of the long alpha-helix in Pf Fd, instead of at the N-terminus of the helix as in Dg Fd. The extensions of the beta-sheets and alpha-helix increase the number of main-chain hydrogen bonds in Pf Fd by approximately 8 relative to those in Dg Fd and likely contribute to its remarkable thermostability (it is unaffected by anaerobic incubation at 95 degrees C for 24 h).(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗

PubMed1993

Effect of high pressure on the association of melittin to membranes.

To determine the underlying basis for the sensitivity of peripheral peptides to lipid packing, we monitored the change in association of melittin to different membranes under hydrostatic pressure by fluorescence polarization and by fluorescence intensity in the presence of aqueous quenchers. Association to lysophosphatidylcholine micelles or to membranes composed of dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine, palmitoyloleoylphosphatidylcholine, or dioleoylphosphatidylcholine was found to be stable from 1 to 2000 atm. Similar results were obtained using multilamellar vesicles, small unilamellar vesicles, or large unilamellar vesicles. Thus, the increase in lipid chain packing induced by pressure does not alter the association of bound complexes. This result indicates similar compressibilities of the peptide and the head group binding region. Increasing the ionic strength to increase the charge of the free peptide also resulted in a pressure-insensitive complex showing that the hydration does not change upon binding. This conclusion is substantiated by a lack of van't Hoff delta H to dioleoylphosphatidylcholine large unilamellar vesicles. To gain a more molecular picture of these associations, the rotational properties of the tryptophan side chain of bound melittin as a function of lipid packing was also studied. These data indicate subtle differences in peptide orientation in different lipids.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1991

Effect of salt and membrane fluidity on fluorophore motions of a gramicidin C derivative.

We have used fluorescence spectroscopy to investigate the effect of salt and membrane fluidity on the rotational motion of a 5-(dimethylamino)naphthalene-1-sulfonyl (dansyl) derivative of gramicidin C (dansyl-gC) in dimyristoylphosphatidylcholine bilayers, under conditions where the peptide is a formyl-NH to formyl-NH terminal dimer, and in octyl glucoside micelles, where the peptide is an intertwined helical dimer. Energy-transfer experiments showed no changes in either conformation or dimer aggregation under the conditions explored here (15-40 degrees C, 1-350 bar, 0-0.33 M Mg2+, and 0-1 M Na+). The addition of permeable (Na+) or nonpermeable (Mg2+) ions did not affect the temperature or pressure behavior of dansyl rotation. However, fluorescence lifetime measurements indicated an increase in solvent accessibility in the presence of sodium. In bilayers, the temperature dependence of the fluorescence polarization and lifetime shows strong interactions between the dansyl residue and the peptide, and at no time did the dansyl motions become solvent controlled as has been observed for aqueous solvent peptides [Scarlata, S. F., Rholam, M., & Weber, G. (1984) Biochemistry 23, 6789]. In micelles, the change in rotational motion with temperature followed solvent expansion, showing that in this case the dansyl residue does not associate extensively with the peptide. Our results indicate that because of the extensive coupling between the dansyl residue and the rest of the peptide, membrane fluidity does not play a major role in controlling side-chain motions.

Amino Acid Sequence↗

PubMed1991

Experimental determination of torsion angles in the polypeptide backbone of the gramicidin A channel by solid state nuclear magnetic resonance.

An analytical method for the determination of torsion angles from solid state 15N nuclear magnetic resonance (n.m.r.) spectroscopic data is demonstrated. Advantage is taken of the 15N-1H and 15N-13C dipolar interactions as well as the 15N chemical shift interaction in oriented samples. The membrane-bound channel conformation of gramicidin A has eluded an atomic resolution structure determination by more traditional approaches. Here, the torsion angles for the Ala3 site are determined by obtaining the n.m.r. data for both the Gly2-Ala3 and Ala3-Leu4 peptide linkages. Complete utilization of the orientational constraints derived from these orientation-dependent nuclear spin interactions in restricting the conformational space is most effectively achieved by utilizing spherical trigonometry. Two possible sets of torsion angles for the Ala3 site are obtained (phi, psi = -129 degrees, 153 degrees and -129 degrees, 122 degrees), both of which are consistent with a right-handed beta-helix. Other functional and computational evidence strongly supports the set for which the carbonyl oxygen atom of the Ala3-Leu4 linkage is rotated into the channel lumen.

Gramicidin↗

PubMed1991

Solid-state nuclear magnetic resonance derived model for dynamics in the polypeptide backbone of the gramicidin A channel.

The dynamics of the backbone of the gramicidin A transmembrane cation channel in dimyristoylphosphatidylcholine bilayers have been investigated using solid state 15N nuclear magnetic resonance (n.m.r.) spectroscopy. With the temperature-dependent fluidity of the bilayer, the rates of motions in the helical gramicidin channel can be modulated. It is shown that in the gel phase, all substantial motions of the channel are slow on the timescale of the n.m.r. experiment (3.5 kHz). The use of oriented samples in which the axis of global channel rotation is aligned parallel to the magnetic field enables separation of global and local dynamics. Spectra obtained from oriented bilayer samples containing single-site 15N-labeled gramicidin at 8 degrees C are analyzed to yield a spatial model for local backbone motion. This model includes the axis of motion, the mean orientation, and the maximum amplitude of displacement for individual peptide planes. Specific sites in the first turn of the amino terminus were investigated, with emphasis on the Ala3 and Leu4 linkages, for which the orientation of the 15N chemical shift tensor with respect to the molecular frame has been determined. The effect of two well-characterized bilayer defect structures, parabolic focal conics and oily streaks, is included in the spectral simulations. It is found that only relatively small amplitude motions are possible at the two sites, with amplitudes of not more than +/- 8 degrees and +/- 15 degrees for the Ala3 and Leu4 sites, respectively. Detailed characterization of the bilayer surface geometry in the oriented samples is presently the major limiting factor in the use of this technique for probing the spatial extent of local motions in integral membrane proteins.

Amino Acid Sequence↗

PubMed1991

Molecular dynamics computations and solid state nuclear magnetic resonance of the gramicidin cation channel.

This paper reports on a coupled approach to determining the structure of the gramicidin A ion channel, utilizing solid state nuclear magnetic resonance (NMR) of isotopically labeled gramicidin channels aligned parallel to the magnetic field direction, and molecular dynamics (MD). MD computations using an idealized right-handed beta-helix as a starting point produce a refined molecular structure that is in excellent agreement with atomic resolution solid state NMR data. The data provided by NMR and MD are complementary to each other. When applied in a coordinated manner they provide a powerful approach to structure determination in molecular systems not readily amenable to x-ray diffraction.

Amino Acid Sequence↗