19F NMR spectroscopy is an attractive and growing area of research with broad applications in biochemistry, chemical biology, medicinal chemistry, and materials science. We have explored fast magic angle spinning (MAS)19F solid‐state NMR spectroscopy in assemblies of HIV‐1 capsid protein. Tryptophan residues with fluorine substitution at the 5‐position of the indole ring were used as the reporters. The19F chemical shifts for the five tryptophan residues are distinct, reflecting differences in their local environment. Spin‐diffusion and radio‐frequency‐driven‐recoupling experiments were performed at MAS frequencies of 35 kHz and 40–60 kHz, respectively. Fast MAS frequencies of 40–60 kHz are essential for consistently establishing19F–19F correlations, yielding interatomic distances of the order of 20 Å. Our results demonstrate the potential of fast MAS19F NMR spectroscopy for structural analysis in large biological assemblies.
To address biophysical principles and lipid interactions that underlie the properties of membrane proteins, modifications that vary the neighbors of tryptophan residues in the highly dynamic transmembrane helix of GW4,20ALP23 (acetyl‐GGAW4A(LA)6LAW20AGA‐amide) were examined using deuterium NMR spectroscopy. It was found that L5,19GW4,20ALP23, a sequence isomer of the low to moderately dynamic GW5,19ALP23, remains highly dynamic. By contrast, a removal of W4 to produce F4,5GW20ALP23 restores a low level of dynamic averaging, similar to that of the F4,5GW19ALP23 helix. Interestingly, a high level of dynamic averaging requires the presence of both tryptophan residues W4 and W20, on opposite faces of the helix, and does not depend on whether residue 5 is Leu or Ala. Aspects of helix unwinding and potential oligomerization are discussed with respect to helix dynamic averaging and the locations of particular residues at a phosphocholine membrane interface.
more » « less- Award ID(s):
- 1713242
- NSF-PAR ID:
- 10453951
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- FEBS Letters
- Volume:
- 594
- Issue:
- 24
- ISSN:
- 0014-5793
- Page Range / eLocation ID:
- p. 4280-4291
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract 19F NMR spectroscopy is an attractive and growing area of research with broad applications in biochemistry, chemical biology, medicinal chemistry, and materials science. We have explored fast magic angle spinning (MAS)19F solid‐state NMR spectroscopy in assemblies of HIV‐1 capsid protein. Tryptophan residues with fluorine substitution at the 5‐position of the indole ring were used as the reporters. The19F chemical shifts for the five tryptophan residues are distinct, reflecting differences in their local environment. Spin‐diffusion and radio‐frequency‐driven‐recoupling experiments were performed at MAS frequencies of 35 kHz and 40–60 kHz, respectively. Fast MAS frequencies of 40–60 kHz are essential for consistently establishing19F–19F correlations, yielding interatomic distances of the order of 20 Å. Our results demonstrate the potential of fast MAS19F NMR spectroscopy for structural analysis in large biological assemblies.
-
more » « less
Abstract The pH‐low insertion peptide (pHLIP) inserts into membranes and forms a transmembrane (TM) α‐helix in response to slight acidity, and has shown great potential for cancer diagnosis and treatment. As a lead, pHLIP is challenging to optimize because the mechanism of its pH‐dependent membrane interactions is not completely understood. Within pHLIP there are multiple D/E residues which could sense the pH change, the particular role played by each of them in the protonation‐driven insertion process is not clear. The precise location of the TM helix within the pHLIP sequence is also unknown. In this work, solid‐state NMR spectroscopy is used to address these central questions. Tracing backbone conformations revealed that the TM helix spans from A10 to D33 with a break at T19 to P20. Residue‐specific p
K avalues of D31, D33, D25, and D14 were determined to be 6.5, 6.3, 6.1, and 5.8, respectively, and define the sequence of protonations which lead to insertion. Furthermore, possible intermediate states which disrupt membranes at pH 6.4 were proposed based on tryptophan fluorescence quenching and NMR data. -
Charged and aromatic amino acid residues, being enriched toward the terminals of membrane-spanning helices in membrane proteins, help to stabilize particular transmembrane orientations. Among them, histidine is aromatic and can be positively charge at low pH. To enable investigations of the underlying protein-lipid interactions, we have examined the effects of single or pairs of interfacial histidine residues using the constructive low-dynamic GWALP23 (acetyl-GG2ALW5LALALALALALALW19LAG22A-amide) peptide framework by incorporating individual or paired histidines at locations 2, 5, 19 or 22. Analysis of helix orientation by means of solid-state 2H NMR spectra of labeled alanine residues reveals marked differences with H2,22 compared to W2,22. Nevertheless, the properties of membrane-spanning H2,22WALP23 helices show little pH dependence and are similar to those having Gly, Arg or Lys at positions 2 and 22. The presence of H5 or H19 influences the helix rotational preference but not the tilt magnitude. H5 affects the helical integrity, as residue 7 unwinds from the core helix; yet once again the helix orientation and dynamic properties show little sensitivity to pH. The overall results reveal that the detailed properties of transmembrane helices depend upon the precise locations of interfacial histidine residues.more » « less
-
more » « less
Lactose permease is a paradigm for the major facilitator superfamily, the largest family of ion-coupled membrane transport proteins known at present. LacY carries out the coupled stoichiometric symport of a galactoside with an H+, using the free energy released from downhill translocation of H+to drive accumulation of galactosides against a concentration gradient. In neutrophilic
Escherichia coli , internal pH is kept at ∼7.6 over the physiological range, but the apparent pK (pKapp) for galactoside binding is 10.5. Surface-enhanced infrared absorption spectroscopy (SEIRAS) demonstrates that the high pKais due to Glu325 (helix X), which must be protonated for LacY to bind galactoside effectively. Deprotonation is also obligatory for turnover, however. Here, we utilize SEIRAS to study the effect of mutating residues in the immediate vicinity of Glu325 on its pKa. The results are consistent with the idea that Arg302 (helix IX) is important for deprotonation of Glu325.
