Rapid estimation of relative amide proton exchange rates of 15 N-labelled proteins by a straightforward water selective NOESY-HSQC experiment

Observation of Fast Two-Dimensional NMR Spectra during Protein Folding Using Polarization Transfer from Hyperpolarized Water

Nuclear spin hyperpolarized water is utilized to obtain protein spectra not only in the folded state but also during the refolding process. Polarization transfer to Ribonuclease Sa through proton exchange and the nuclear Overhauser effect (NOE) results in NMR signal enhancements of amide protons by up to 24-fold. These enhancements enable the measurement of fast two-dimensional NMR spectra on the same time scale as the folding. Resolved amide proton signals corresponding to the folded protein are observed both under folded and refolding conditions, whereby the refolding protein shows smaller transferred signals. Residue-specific evaluation of contributions to the polarization transfer indicates that signals attributed to a relayed intramolecular NOE are not observable in the refolding experiment. These differences are explained by the absence of long-range contacts and faster molecular motions in the unfolded protein. Applications of this method include accessing residue-specific information on structure and dynamics during multistate protein folding.

Measurement of amide hydrogen exchange rates with the use of radiation damping

A simple method for measuring amide hydrogen exchange rates is presented, which is based on the selective inversion of water magnetization with the use of radiation damping. Simulations show that accurate exchange rates can be measured despite the complications of radiation damping and cross relaxation to the exchange process between amide and water protons. This method cannot eliminate the contributions of the exchange-relayed NOE and direct NOE to the measured exchange rates, but minimize the direct NOE contribution. In addition, the amides with a significant amount of such indirect contributions are possible to be identified from the shape of the exchange peak intensity profiles or/and from the apparent relaxation rates of amide protons which are extracted from fitting the intensity profiles to an equation established here for our experiment. The method was tested on ubiquitin and also applied to an acyl carrier protein. The amide exchange rates for the acyl carrier protein at two pHs indicate that the entire protein is highly dynamic on the second timescale. Low protection factors for the residues in the regular secondary structural elements also suggest the presence of invisible unfolded species. The highly dynamic nature of the acyl carrier protein may be crucial for its interactions with its substrate and enzymes.

An introduction to NMR-based approaches for measuring protein dynamics

Proteins are inherently flexible at ambient temperature. At equilibrium, they are characterized by a set of conformations that undergo continuous exchange within a hierarchy of spatial and temporal scales ranging from nanometers to micrometers and femtoseconds to hours. Dynamic properties of proteins are essential for describing the structural bases of their biological functions including catalysis, binding, regulation and cellular structure. Nuclear magnetic resonance (NMR) spectroscopy represents a powerful technique for measuring these essential features of proteins. Here we provide an introduction to NMR-based approaches for studying protein dynamics, highlighting eight distinct methods with recent examples, contextualized within a common experimental and analytical framework. The selected methods are (1) Real-time NMR, (2) Exchange spectroscopy, (3) Lineshape analysis, (4) CPMG relaxation dispersion, (5) Rotating frame relaxation dispersion, (6) Nuclear spin relaxation, (7) Residual dipolar coupling, (8) Paramagnetic relaxation enhancement. This article is part of a Special Issue entitled: Protein Dynamics: Experimental and Computational Approaches.

Water-protein hydrogen exchange in the micro-crystalline protein crh as observed by solid state NMR spectroscopy

We report site-resolved observation of hydrogen exchange in the micro-crystalline protein Crh. Our approach is based on the use of proton T2' -selective 1H-13C-13C correlation spectra for site-specific assignments of carbons nearby labile protein protons. We compare the proton T2' selective scheme to frequency selective water observation in deuterated proteins, and discuss the impacts of deuteration on 13C linewidths in Crh. We observe that in micro-crystalline proteins, solvent accessible hydroxyl and amino protons show comparable exchange rates with water protons as for proteins in solution, and that structural constraints, such as hydrogen bonding or solvent accessibility, more significantly reduce exchange rates.

Water−Protein Interactions in Microcrystalline Crh Measured by 1H−13C Solid-State NMR Spectroscopy

Using solid-state NMR carbon-proton dipolar correlation spectroscopy, we observed hydrogen exchange on the millisecond time scale between water molecules and protein protons in a solid sample. These interactions are shown to be related to important structural features of the protein such as hydrogen-bonding or salt-bridge networks.

Protein hydration and location of water molecules in oxidized horse heart cytochrome c by (1)H NMR

The hydration properties of the oxidized form of horse heart cytochrome c have been studied by (1)H NMR spectroscopy. Two-dimensional, homonuclear ePHOGSY-NOESY experiments are used to map water-protein interactions. The detected NOEs reveal interactions between nonexchangeable protein protons and both water protons and labile protein protons which exchange with water protons. Among the many water molecules apparent in the X-ray structure, three have been identified with a residence time longer than 300 ps. One of them is located inside the distal heme cavity, in the deepest part of a hydration pathway extending toward the surface. The identification of hydrophilic regions and detection of three long-lived water molecules settles some ambiguities and provides a better representation of the water-protein interactions in oxidized cytochrome c.

Determination of fast proton exchange rates of biomolecules by NMR using water selective diffusion experiments

We present a new water selective pulse sequence allowing rapid determination of exchange rates of labile protons on the millisecond time scale. Using diffusion measurements, exchange rates of resolved protons can be determined without prior knowledge of relaxation parameters in a short overnight experiment. The use of a sensitive, highly selective and easy to implement water excitation scheme allows for its straightforward application to a wide range of biomolecules. The results obtained for the imino proton exchange rates of a 16 bp DNA are in strong agreement with values obtained by the classical approach of two-dimensional exchange spectroscopy.

ePHOGSY experiments on a paramagnetic protein: location of the catalytic water molecule in the heme crevice of the oxidized form of horse heart cytochrome c

The hydration properties of the oxidized form of horse heart cytochrome c have been studied by 1H NMR spectroscopy. Application of ePHOGSY (enhanced protein hydration observed through gradient spectroscopy) experiments over a paramagnetic molecule provided firm spectroscopic evidence of the presence of a water molecule in the heme crevice. A few intermolecular NOEs have been used to locate the water molecule at about 0.65 nm away from the iron atom and to compare the position observed in solution with that observed in the crystal structure and in solution for the reduced state. The resulting picture is that there is a detectable movement of the water molecule upon oxidation.

Three-dimensional structure of the DNA-binding domain of the fructose repressor from Escherichia coli by 1H and 15N NMR

FruR is an Escherichia coli transcriptional regulator that belongs to the LacI DNA-binding protein family. By using 1H and 15N NMR spectroscopy, we have determined the three-dimensional solution structure of the FruR N-terminal DNA-binding domain consisting of 57 amino acid residues. A total of 809 NMR-derived distances and 54 dihedral angle constraints have been used for molecular modelling with the X-PLOR program. The resulting set of calculated structures presents an average root-mean-square deviation of 0.37 A at the main-chain level for the first 47 residues. This highly defined N-terminal part of the structure reveals a similar topology for the three alpha-helices when compared to the 3D structures of LacI and PurR counterparts. The most striking difference lies in the connection between helix II and helix III, in which three additional residues are present in FruR. This connecting segment is well structured and contains a type III turn. Apart from hydrophobic interactions of non-polar residues with the core of the domain, this connecting segment is stabilised by several hydrogen bonds and by the aromatic ring stacking between Tyr19 of helix II and Tyr28 of the turn. The region containing the putative "hinge helix" (helix IV), that has been described in PurR-DNA complex to make specific base contacts in the minor groove of DNA, is unfolded. Examination of hydrogen bonds highlights the importance of homologous residues that seem to be conserved for their ability to fulfill helix N and C-capping roles in the LacI repressor family.