The dependence of signal-to-noise ratio on number of scans in covariance spectroscopy

PYK2 senses calcium through a disordered dimerization and calmodulin-binding element

Multidomain kinases use many ways to integrate and process diverse stimuli. Here, we investigated the mechanism by which the protein tyrosine kinase 2-beta (PYK2) functions as a sensor and effector of cellular calcium influx. We show that the linker between the PYK2 kinase and FAT domains (KFL) encompasses an unusual calmodulin (CaM) binding element. PYK2 KFL is disordered and engages CaM through an ensemble of transient binding events. Calcium increases the association by promoting structural changes in CaM that expose auxiliary interaction opportunities. KFL also forms fuzzy dimers, and dimerization is enhanced by CaM binding. As a monomer, however, KFL associates with the PYK2 FERM-kinase fragment. Thus, we identify a mechanism whereby calcium influx can promote PYK2 self-association, and hence kinase-activating trans-autophosphorylation. Collectively, our findings describe a flexible protein module that expands the paradigms for CaM binding and self-association, and their use for controlling kinase activity.

Protein tyrosine kinase 2-beta is shown to function as a sensor and effector of cellular calcium influx through self-association.

Hadamard acquisition of 13 C-13 C 2-D correlation NMR spectra

We show that a multiselective excitation with Hadamard encoding is a powerful tool for 2-D acquisition of ¹³ C─¹³ C homonuclear correlations. This method is not designed to improve the sensitivity, but rather to reduce the experiment time, provided there is sufficient sensitivity. Therefore, it allows fast acquisition of such 2-D spectra in labeled molecules. The technique has been demonstrated using a U─¹³ C─¹⁵ N histidine hydrochloride monohydrate sample allowing each point of the build-up curves of the ¹³ C─¹³ C cross-peaks to be recorded within 4 min 35 s, which is very difficult with conventional methods. Using the U─¹³ C─¹⁵ N f-MLF sample, we have demonstrated that the method can be applied to molecules with 14 ¹³ C resonances with a minimum frequency separation of 240 Hz.

Recording 13C-15N HMQC 2D sparse spectra in solids in 30 s

We propose a dipolar HMQC Hadamard-encoded (D-HMQC-H_n) experiment for fast 2D correlations of abundant nuclei in solids. The main limitation of the Hadamard methods resides in the length of the encoding pulses, which results from a compromise between the selectivity and the sensitivity due to losses. For this reason, these methods should mainly be used with sparse spectra, and they profit from the increased separation of the resonances at high magnetic fields. In the case of the D-HMQC-H_n experiments, we give a simple rule that allows directly setting the optimum length of the selective pulses, versus the minimum separation of the resonances in the indirect dimension. The demonstration has been performed on a fully ¹³C,¹⁵N labelled f-MLF sample, and it allowed recording the build-up curves of the ¹³C-¹⁵N cross-peaks within 10 min. However, the method could also be used in the case of less sensitive samples, but with more accumulations.

Fast acquisition of multidimensional NMR spectra of solids and mesophases using alternative sampling methods

Unique information about the atom-level structure and dynamics of solids and mesophases can be obtained by the use of multidimensional nuclear magnetic resonance (NMR) experiments. Nevertheless, the acquisition of these experiments often requires long acquisition times. We review here alternative sampling methods, which have been proposed to circumvent this issue in the case of solids and mesophases. Compared to the spectra of solutions, those of solids and mesophases present some specificities because they usually display lower signal-to-noise ratios, non-Lorentzian line shapes, lower spectral resolutions and wider spectral widths. We highlight herein the advantages and limitations of these alternative sampling methods. A first route to accelerate the acquisition time of multidimensional NMR spectra consists in the use of sparse sampling schemes, such as truncated, radial or random sampling ones. These sparsely sampled datasets are generally processed by reconstruction methods differing from the Discrete Fourier Transform (DFT). A host of non-DFT methods have been applied for solids and mesophases, including the G-matrix Fourier transform, the linear least-square procedures, the covariance transform, the maximum entropy and the compressed sensing. A second class of alternative sampling consists in departing from the Jeener paradigm for multidimensional NMR experiments. These non-Jeener methods include Hadamard spectroscopy as well as spatial or orientational encoding of the evolution frequencies. The increasing number of high field NMR magnets and the development of techniques to enhance NMR sensitivity will contribute to widen the use of these alternative sampling methods for the study of solids and mesophases in the coming years.