Matthias Görlach

Interaction of the RNA-binding domain of the hnRNP C proteins with RNA.

The hnRNP C proteins are among the most abundant and avid pre‐mRNA‐binding proteins and they contain a consensus sequence RNA‐binding domain (RBD) that is found in a large number of RNA‐binding proteins. The interaction of the RBD of the hnRNP C proteins with an RNA oligonucleotide [r(U)8] was monitored by nuclear magnetic resonance (NMR). 15N and 13C/15N‐labelled hnRNP C protein RBD was mixed with r(U)8 and one‐ and two‐dimensional (1D and 2D) NMR spectra were recorded in a titration experiment. NMR studies of the uncomplexed 93 amino acid hnRNP C RBD (Wittekind et al., 1992) have shown that it has a compact folded structure (beta alpha beta beta alpha beta), which is typical for the RBD of this family of proteins and which is comprised of a four‐stranded antiparallel beta‐sheet, two alpha‐helices and relatively unstructured amino‐ and carboxy‐terminal regions. Sequential assignments of the polypeptide main‐chain atoms of the hnRNP C RBD‐r(U)8 complex revealed that these typical structural features are maintained in the complex, but significant perturbations of the chemical shifts of amide group atoms occur in a large number of residues. Most of these residues are in the beta‐sheet region and especially in the terminal regions of the RBD. In contrast; chemical shifts of the residues of the well conserved alpha‐helices, with the exception of Lys30, are not significantly perturbed. These observations localize the candidate residues of the RBD that are involved in the interaction with the RNA.(ABSTRACT TRUNCATED AT 250 WORDS)

The NMR structure of Escherichia coli ribosomal protein L25 shows homology to general stress proteins and glutaminyl‐tRNA synthetases

The structure of the Escherichia coli ribosomal protein L25 has been determined to an r.m.s. displacement of backbone heavy atoms of 0.62 ± 0.14 Å by multi‐dimensional heteronuclear NMR spectroscopy on protein samples uniformly labeled with 15N or 15N/13C. L25 shows a new topology for RNA‐binding proteins consisting of a six‐stranded β‐barrel and two α‐helices. A putative RNA‐binding surface for L25 has been obtained by comparison of backbone 15N chemical shifts for L25 with and without a bound cognate RNA containing the eubacterial E‐loop that is the site for binding of L25 to 5S ribosomal RNA. Sequence comparisons with related proteins, including the general stress protein, CTC, show that the residues involved in RNA binding are highly conserved, thereby providing further confirmation of the binding surface. Tertiary structure comparisons indicate that the six‐stranded β‐barrels of L25 and of the tRNA anticodon‐binding domain of glutaminyl‐tRNA synthetase are similar.

The hnRNP proteins

ConclusionsThe isolation of hnRNP complexes has identified many new proteins and their characterization has led to the identification of several motifs that are important for RNA binding. These motifs are present in a wide variety of proteins including splicing factors, ribosomal proteins, and several proteins of unknown function. These findings have blurred the lines of demarcation between proteins previously thought of as RNA “packaging” proteins and RNA processing factors. Recent findings on hnRNP proteins have suggested a plethora of possible functions along the pathway of mRNA metabolism. It can be expected that the next few years will see the unraveling of the detailed functions of hnRNP proteins.

Solid state NMR of proteins at high MAS frequencies: symmetry-based mixing and simultaneous acquisition of chemical shift correlation spectra

We have carried out chemical shift correlation experiments with symmetry-based mixing sequences at high MAS frequencies and examined different strategies to simultaneously acquire 3D correlation spectra that are commonly required in the structural studies of proteins. The potential of numerically optimised symmetry-based mixing sequences and the simultaneous recording of chemical shift correlation spectra such as: 3D NCAC and 3D NHH with dual receivers, 3D NC′C and 3D C′NCA with sequential 13C acquisitions, 3D NHH and 3D NC′H with sequential 1H acquisitions and 3D CANH and 3D C’NH with broadband 13C–15N mixing are demonstrated using microcrystalline samples of the β1 immunoglobulin binding domain of protein G (GB1) and the chicken α-spectrin SH3 domain.

Conformational signatures of 13C chemical shifts in RNA ribose

The conformational dependence of 13C chemical shift values of RNA riboses determined by liquid-state NMR spectroscopy was evaluated using data deposited for RNA structures in the RCSD and BMRB data bases. Results derived support the applicability of the canonical coordinates approach of Rossi and Harbison (J Magn Reson 151:1–8, 2001) in liquid-state NMR to assess the sugar pucker of ribose units in RNA.

Solution structure of stem-loop α of the hepatitis B virus post-transcriptional regulatory element

Chronic hepatitis B virus (HBV) infections may lead to severe diseases like liver cirrhosis or hepatocellular carcinoma (HCC). The HBV post-transcriptional regulatory element (HPRE) facilitates the nuclear export of unspliced viral mRNAs, contains a splicing regulatory element and resides in the 3′-region of all viral transcripts. The HPRE consists of three sub-elements α (nucleotides 1151–1346), β1 (nucleotides 1347–1457) and β2 (nucleotides 1458–1582), which confer together full export competence. Here, we present the NMR solution structure (pdb 2JYM) of the stem-loop α (SLα, nucleotides 1292–1321) located in the sub-element α. The SLα contains a CAGGC pentaloop highly conserved in hepatoviruses, which essentially adopts a CUNG-like tetraloop conformation. Furthermore, the SLα harbours a single bulged G residue flanked by A-helical regions. The structure is highly suggestive of serving two functions in the context of export of unspliced viral RNA: binding sterile alpha motif (SAM-) domain containing proteins and/or preventing the utilization of a 3′-splice site contained within SLα.

Chemical shift correlation at high MAS frequencies employing low-power symmetry-based mixing schemes

An approach for conveniently implementing low-power CNnν and RNnν symmetry-based band-selective mixing sequences for generating homo- and heteronuclear chemical shift correlation NMR spectra of low γ nuclei in biological solids is demonstrated. Efficient magnetisation transfer characteristics are achieved by selecting appropriate symmetries requiring the application of basic RF elements of relatively long duration and numerically tailoring the RF field modulation profile of the basic element. The efficacy of the approach is experimentally shown by the acquisition of 15N–13C dipolar and 13C–13C scalar and dipolar coupling mediated chemical shift correlation spectra at representative MAS frequencies.

RFDR with Adiabatic Inversion Pulses: Application to Internuclear Distance Measurements

In the context of the structural characterisation of biomolecular systems via MAS solid state NMR, the potential utility of homonuclear dipolar recoupling with adiabatic inversion pulses has been assessed via numerical simulations and experimental measurements. The results obtained suggest that it is possible to obtain reliable estimates of internuclear distances via an analysis of the initial cross-peak intensity buildup curves generated from two-dimensional adiabatic inversion pulse driven longitudinal magnetisation exchange experiments.

Recoupling and decoupling of nuclear spin interactions at high MAS frequencies: numerical design of CNnν symmetry-based RF pulse schemes

The CNnν class of RF pulse schemes, commonly employed for recoupling and decoupling of nuclear spin interactions in magic angle spinning solid state NMR studies of biological systems, involves the application of a basic “C” element corresponding to an RF cycle with unity propagator. In this study, the design of CNnν symmetry-based RF pulse sequences for achieving 13C–13C double-quantum dipolar recoupling and through bond scalar coupling mediated 13C–13C chemical shift correlation has been examined at high MAS frequencies employing broadband, constant-amplitude, phase-modulated basic “C” elements. The basic elements were implemented as a sandwich of a small number of short pulses of equal duration with each pulse characterised by an RF phase value. The phase-modulation profile of the “C” element was optimised numerically so as to generate efficient RF pulse sequences. The performances of the sequences were evaluated via numerical simulations and experimental measurements and are presented here.

Structure–function relationship in an archaebacterial methionine sulphoxide reductase B

Oxidation of methionine to methionine sulphoxide (MetSO) may lead to loss of molecular integrity and function. This oxidation can be ‘repaired’ by methionine sulphoxide reductases (MSRs), which reduce MetSO back to methionine. Two structurally unrelated classes of MSRs, MSRA and MSRB, show stereoselectivity towards the S and the R enantiomer of the sulphoxide respectively. Interestingly, these enzymes were even maintained throughout evolution in anaerobic organisms. Here, the activity and the nuclear magnetic resonance (NMR) structure of MTH711, a zinc containing MSRB from the thermophilic, methanogenic archaebacterium Methanothermobacter thermoautotrophicus, are described. The structure appears more rigid as compared with similar MSRBs from aerobic and mesophilic organisms. No significant structural differences between the oxidized and the reduced MTH711 state can be deduced from our NMR data. A stable sulphenic acid is formed at the catalytic Cys residue upon oxidation of the enzyme with MetSO. The two non‐zinc‐binding cysteines outside the catalytic centre are not necessary for activity of MTH711 and are not situated close enough to the active‐site cysteine to serve in regenerating the active centre via the formation of an intramolecular disulphide bond. These findings imply a reaction cycle that differs from that observed for other MSRBs.