Biomedical subjects
Publications and source records attributed to Bernhard Brutscher.
We demonstrate for different protein samples that three-dimensional HNCO and HNCA correlation spectra may be recorded in a few minutes acquisition time using the band-selective excitation short-transient sequences presented here. This opens new perspectives for the NMR structural investigation of unstable protein samples and real-time site-resolved studies of protein kinetics.
Ferric uptake regulator (Fur) is a global bacterial regulator that uses iron as a cofactor to bind to specific DNA sequences. Escherichia coli Fur is usually isolated as a homodimer with two metal sites per subunit. Metal binding to the iron site induces protein activation; however the exact role of the structural zinc site is still unknown. Structural studies of three different forms of the Escherichia coli Fur protein (nonactivated dimer, monomer, and truncated Fur-(1-82)) were performed. Dimerization of the oxidized monomer was followed by NMR in the presence of a reductant (dithiothreitol) and Zn(II). Reduction of the disulfide bridges causes only local structure variations, whereas zinc addition to reduced Fur induces protein dimerization. This demonstrates for the first time the essential role of zinc in the stabilization of the quaternary structure. The secondary structures of the mono- and dimeric forms are almost conserved in the N-terminal DNA-binding domain, except for the first helix, which is not present in the nonactivated dimer. In contrast, the C-terminal dimerization domain is well structured in the dimer but appears flexible in the monomer. This is also confirmed by heteronuclear Overhauser effect data. The crystal structure at 1.8A resolution of a truncated protein (Fur-(1-82)) is described and found to be identical to the N-terminal domain in the monomeric and in the metal-activated state. Altogether, these data allow us to propose an activation mechanism for E. coli Fur involving the folding/unfolding of the N-terminal helix.
Structure elucidation of proteins by either NMR or X-ray crystallography often requires the screening of a large number of samples for promising protein constructs and optimum solution conditions. For large-scale screening of protein samples in solution, robust methods are needed that allow a rapid assessment of the folding of a polypeptide under diverse sample conditions. Here we present HET-SOFAST NMR, a highly sensitive new method for semi-quantitative characterization of the structural compactness and heterogeneity of polypeptide chains in solution. On the basis of one-dimensional 1H HET-SOFAST NMR data, obtained on well-folded, molten globular, partially- and completely unfolded proteins, we define empirical thresholds that can be used as quantitative benchmarks for protein compactness. For 15N-enriched protein samples, two-dimensional 1H-15N HET-SOFAST correlation spectra provide site-specific information about the structural heterogeneity along the polypeptide chain.
We demonstrate the feasibility of recording (1)H-(15)N correlation spectra of proteins in only one second of acquisition time. The experiment combines recently proposed SOFAST-HMQC with Hadamard-type (15)N frequency encoding. This allows site-resolved real-time NMR studies of kinetic processes in proteins with an increased time resolution. The sensitivity of the experiment is sufficient to be applicable to a wide range of molecular systems available at millimolar concentration on a high magnetic field spectrometer.
The flavoprotein moiety of Escherichia coli sulfite reductase (SiR-FP) is homologous to electron transfer proteins such as cytochrome-P450 reductase (CPR) or nitric oxide synthase (NOS). We report on the three-dimensional structure of SiR-FP18, the flavodoxin-like domain of SiR-FP, which has been determined by NMR. In the holoenzyme, this domain plays an important role by shuttling electrons from the FAD to the hemoprotein (the beta-subunit). The structure presented here was determined using distance and torsion angle information in combination with residual dipolar couplings determined in two different alignment media. Several protein-FMN NOEs allowed us to place the prosthetic group in its binding pocket. The structure is well-resolved, and (15)N relaxation data indicate that SiR-FP18 is a compact domain. The binding interface with cytochrome c, a nonphysiological electron acceptor, has been determined using chemical shift mapping. Comparison of the SiR-FP18 structure with the corresponding domains from CPR and NOS shows that the fold of the protein core is highly conserved, but the analysis of the electrostatic surfaces reveals significant differences between the three domains. These observations are placed in the physiological context so they can contribute to the understanding of the electron transfer mechanism in the SiR holoenzyme.
We demonstrate for different protein samples that 2D 1H-15N correlation NMR spectra can be recorded in a few seconds of acquisition time using a new band-selective optimized flip-angle short-transient heteronuclear multiple quantum coherence experiment. This has enabled us to measure fast hydrogen-deuterium exchange rate constants along the backbone of a small globular protein fragment by real-time 2D NMR.
Fast multidimensional NMR with a time resolution of a few seconds provides a new tool for high throughput screening and site-resolved real-time studies of kinetic molecular processes by NMR. Recently we have demonstrated the feasibility to record protein 1H-15N correlation spectra in a few seconds of acquisition time using a new SOFAST-HMQC experiment (Schanda and Brutscher (2005) J. Am. Chem. Soc. 127, 8014). Here, we investigate in detail the performance of SOFAST-HMQC to record 1H-15N and 1H-13C correlation spectra of proteins of different size and at different magnetic field strengths. Compared to standard 1H-15N correlation experiments SOFAST-HMQC provides a significant gain in sensitivity, especially for fast repetition rates. Guidelines are provided on how to set up SOFAST-HMQC experiments for a given protein sample. In addition, an alternative pulse scheme, IPAP-SOFAST-HMQC is presented that allows application on NMR spectrometers equipped with cryogenic probes, and fast measurement of one-bond 1H-13C and 1H-15N scalar and residual dipolar coupling constants.
New base-type-edited transverse-relaxation optimized CT-HCN(C) experiments are presented that yield intra-base and sugar-to-base correlations for 13C-15N labeled RNA. High spectral resolution in the 13C and 15N dimensions is achieved by constant time (CT) frequency editing. A spectral editing filter applied during the CT 15N labeling period separates the correlation peaks arising from G/U and A/C nucleotide bases. This provides the increased spectral resolution required to unambiguously connect the 1H and 13C resonances in sugar and base moieties of RNA nucleotides. In addition, the experiment allows base type identification for each residue, and therefore presents an attractive spectroscopic alternative to nucleotide-specific isotope labeling. Application to a 33-nucleotide RNA aptamer demonstrates the performance of the new pulse scheme.
New NMR experiments are presented for the measurement of methyl-methyl distances in (13)C-labeled proteins from a series of amino acid-type separated 2D or 3D NOESY spectra. Hadamard amino acid-type encoding of the proximal methyl groups provides the high spectral resolution required for unambiguous methyl-methyl NOE assignment, which is particularly important for fast global fold determination of proteins. The experiments can be applied to a wide range of protein systems, as exemplified for two small proteins, ubiquitin and MerAa, and the 30 kDa BRP-Blm complex.
2D DEPT-H(alpha,beta)C(alpha,beta)(CO)NH and 2D CT-DEPT-HC(CO)NH-TOCSY experiments are presented which allow fast resonance assignment of aliphatic protein side chains. In these 2D reduced-dimensionality experiments, two or three nuclei are frequency labeled in the indirect dimension. DEPT spectral editing reduces the number of correlation peaks detected in each 2D spectrum, and helps in amino-acid-type determination during sequential backbone resonance assignment. Applications are shown for a small 68-residue, and a highly deuterated 167-residue protein. The new experiments complement the set of 2D HNX correlation experiments, previously proposed for fast protein resonance assignment [J. Biomol. NMR, 27 (2003) 57].
A detailed theoretical and experimental analysis of the artifacts induced by homonuclear band-selective decoupling during CT frequency labeling is presented. The effects are discussed in the context of an amino-acid-type editing filter implemented in (1)H-(13)C CT-HSQC experiments of methyl groups in proteins. It is shown that both Bloch-Siegert shifts and modulation sidebands are efficiently suppressed by using additional off-resonance decoupling as proposed by Zhang and Gorenstein [J. Magn. Reson. 132 (1998) 81], and appropriate adjustment of a set of pulse sequence parameters. The theoretical predictions are confirmed by experiments performed on (13)C-labeled protein samples, yielding artifact-free amino-acid-type edited methyl spectra.
A simple and general method is presented to simplify multi-dimensional NMR spectra of isotope-labeled bio-molecules. The approach is based on band-selective Hadamard-type frequency encoding, which disperses the correlation peaks into different sub-spectra. This makes it possible to apply low-dimensionality-based NMR techniques to larger molecular systems. Here we demonstrate the use of band-selective Hadamard frequency labeling for fast protein resonance assignment, based on our recently proposed suite of 2D experiments (Bersch et al., 2003).
The purified native mercuric reductase (MerA) from Ralstonia metallidurans CH34 contains an N-terminal sequence of 68 amino acids predicted to be homologous to MerP, the periplasmic mercury-binding protein. This MerP-like protein has now been expressed independently. The protein was named MerAa by homology with Ccc2a, the first soluble domain of the copper-transporting ATPase from yeast. Deltaa has been characterized using a set of biophysical techniques. The binding of mercury was followed using circular dichroism spectroscopy and electrospray mass spectrometry. The two cysteine residues contained in the consensus sequence GMTC XXC are involved in the binding of one mercury atom, with an apparent affinity comparable to that of MerP for the same metal. The metal-binding site is confirmed by NMR chemical shift changes observed between apo- and metal-bound MerAa in solution. NMR shift and NOE data also indicate that only minor structural changes occur upon metal binding. Further NMR investigation of the fold of MerAa using long-range methyl-methyl NOE and backbone residual dipolar coupling data confirm the expected close structural homology with MerP. (15)N relaxation data show that MerAa is a globally rigid molecule. An increased backbone mobility was observed for the loop region connecting the first beta-strand and the first alpha-helix and comprising the metal-binding domain. Although significantly reduced, this loop region keeps some conformational flexibility upon metal binding. Altogether, our data suggest a role of MerAa in mercury trafficking.
We show that the resolution of homonuclear multidimensional solid-state NMR correlation experiments can be significantly improved using transition selection and spin-state-selective polarization transfer techniques. The selection and transfer of single states allow the removal of the J-coupling contribution from the line width in both the direct and indirect spectral dimensions. This is demonstrated with a new spin-state-selective CO-Calpha correlation experiment, applied to a microcrystalline 85-residue protein. With this new sequence, all four components of the CO-Calpha cross-peaks are separated into different spectra, obtained by linear combination of four recorded data sets. Line narrowing of up to 44% was obtained on the protein sample for the spin-state-selective CO-Calpha spectrum compared to a standard spin-diffusion experiment. The new technique also allows an easy distinction between "direct" and "relayed" transfer cross-peaks.
In mammals, numerous precursors of antibacterial peptides with unrelated sequences share a similar prosequence of 94-114 residues, termed the cathelin-like domain. The cathelin-like domain of protegrin-3 (ProS) was overexpressed in Escherichia coli and uniformly labeled with (15)N or (15)N and (13)C, and its three-dimensional structure was determined by heteronuclear NMR at pH 6.2. Under these conditions and due to the cis-trans isomerization of the R(87)-P(88) and D(118)-P(119) amide bonds, the ProS structure was found to adopt four almost equally populated conformations in slow exchange on the NMR chemical shift time scale. The ProS structure consists of an N-terminal alpha-helix (Y(34)-N(48)) cradled by a four-stranded antiparallel beta-sheet (beta1, N(53)-L(60); beta2, K(74)-P(86); beta3, V(104)-V(111); and beta4, I(122)-C(124)). The solution structure of ProS, which is monomeric, allowed us to determine the structure of the L1 and L2 loops, which are too mobile in the crystal structure. The regions common to the solution and X-ray structures were found to be very similar. Finally, since the overall fold of ProS is very similar to that of cystatins despite a low degree of sequence identity, the ProS solution structure was compared to the solution and X-ray structures of the chicken cystatin. This comparison revealed that the structures of the L1 and L2 loops as well as that of the appending domain are quite different in the two proteins. These differences are mainly due to the high proline residue content (10%) which disorganizes the hydrogen bond network of a part of the ProS beta-sheet in contrast to that of the chicken cystatin structure.
Bleomycin (Bm), a 1.4 kDa glycopeptide excreted by Streptomyces verticillus, is a natural antibacterial compound used in therapy as antineoplastic drug. To counteract its biological activity, cells have developed several resistance mechanisms, one of these based on proteins able to tightly bind Bm. In this paper, the interaction of Zn(2+)-Bm with the Streptoalloteichus hindustanus Bm resistance protein (ShBle) has been investigated by solution state NMR. Sequential nOe and chemical shift index have shown that the fold of the protein (in absence or presence of Bm) is identical to the previously published X-ray structure. The dimeric nature of ShBle is confirmed by the diffusion tensor as determined by NMR relaxation data. Using isotope filtered nOe experiment, intermolecular nOes between Bm and ShBle have been observed as used for modeling. While the interaction of the Bm metal binding site with ShBle appears to be uniquely defined, several conformations of the bithiazole moieties are compatible with the NMR data. Binding of Bm also induces changes of the local dynamics (stretch N85-G91), as shown by (15)N relaxation data. These results are discussed in the context of several Bm analogues able to interact with ShBle and of the recently published X-rays structures.
NMR experiments are presented which allow backbone resonance assignment, secondary structure identification, and in favorable cases also molecular fold topology determination from a series of two-dimensional 1H-15N HSQC-like spectra. The 1H-15N correlation peaks are frequency shifted by an amount +/- omegaX along the 15N dimension, where omegaX is the Calpha, Cbeta, or Halpha frequency of the same or the preceding residue. Because of the low dimensionality (2D) of the experiments, high-resolution spectra are obtained in a short overall experimental time. The whole series of seven experiments can be performed in typically less than one day. This approach significantly reduces experimental time when compared to the standard 3D-based methods. The here presented methodology is thus especially appealing in the context of high-throughput NMR studies of protein structure, dynamics or molecular interfaces.
High-level deuteration is a prerequisite for the study of high molecular weight systems using liquid-state NMR. Here, we present new experiments for the measurement of proton-proton dipolar couplings in CH(2)D methyl groups of (13)C labeled, highly deuterated (70-80%) proteins. (1)H-(1)H residual dipolar couplings (RDCs) have been measured in two alignment media for 57 out of 70 possible methyl containing residues in the 167-residue flavodoxin-like domain of the E. coli sulfite reductase. These data yield information on the orientation of the methyl symmetry axis with respect to the molecular alignment frame. The alignment tensor characteristics were obtained very accurately from a set of backbone RDCs measured on the same protein sample. To demonstrate that accurate structural information is obtained from these data, the measured methyl RDCs for Valine residues are analyzed in terms of chi(1) torsion angles and stereospecific assignment of the prochiral methyl groups. On the basis of the previously determined backbone solution structure of this protein, the methyl RDC data proved sufficient to determine the chi(1) torsion angles in seven out of nine valines, assuming a single-rotamer model. Methyl RDCs are complementary to other NMR data, for example, methyl-methyl NOE, to determine side chain conformation in high molecular weight systems.