Experimental setup of the MAS solid-state NMR experiment of insoluble proteins.

(A) The sample is placed inside a rotor that is oriented at 54.7° with respect to the static magnetic field and rotated within a solenoid coil, which allows the application of rf pulses to manipulate nuclear magnetization. Upon sample rotation, molecules experience periodical modulations of the rf field due to spatial inhomogeneity. Magnetic field lines are drawn schematically. (B) Protein molecules are contained in microcrystals that are randomly oriented in a powder. (C) Atomic level protein structure with arrows illustrating NCA and NCO magnetization transfer pathways between the amide nitrogen and Cα/C′ carbons (NCA/NCO transfers) of the protein backbone. The relative orientation of a bond vector with respect to the external static magnetic field determines the size of the dipolar interaction between the two atoms. The scale on the right indicates typical order of magnitude for object dimensions.

 Zdeněk Tošner and Bernd Reif Research Groups

Significance

Dipolar recoupling is a central concept in the nuclear magnetic resonance spectroscopy of powdered solids and is used to establish correlations between different nuclei by magnetization transfer. The efficiency of conventional cross-polarization methods is low because of the inherent radio frequency (rf) field inhomogeneity present in the magic angle spinning (MAS) experiments and the large chemical shift anisotropies at high magnetic fields. Very high transfer efficiencies can be obtained using optimal control–derived experiments. These sequences had to be optimized individually for a particular MAS frequency. We show that by adjusting the length and the rf field amplitude of the shaped pulse synchronously with sample rotation, optimal control sequences can be successfully applied over a range of MAS frequencies without the need of reoptimization. This feature greatly enhances their applicability on spectrometers operating at differing external fields where the MAS frequency needs to be adjusted to avoid detrimental resonance effects.

Tosner, Z., Brandl, M.J., Blahut, J., Glaser, S.J., and Reif, B.: Maximizing efficiency of dipolar recoupling in solid-state NMR using optimal control sequences, Sci. Adv. 2021, 7(42), abj5913, https://doi.org/10.1126/sciadv.abj5913

Structural characterization of the PSMA/Glu-490 complex

a Molecular formula of the Glu-490. b A stereo view of the Gluo-490 inhibitor. The Fo-Fc omit map (green) is contoured at 3.0 σ and the inhibitor is shown in stick representation with atoms colored red (oxygen), blue (nitrogen), yellow (sulfur), and cyan (carbon). c Details of interactions between residues of the glutarate sensor (green carbons) and Glu-490 (cyan carbons). CH–π interactions are depicted as dashed lines with distances to the ring centers in Angstroms. The active-site zinc ions are shown as orange spheres. d Surface representation of PSMA with residues of the glutarate sensor interaction with the FMR moiety colored blue, PDB code (7BFZ).

Yiguang Wang, Cyril Bařinka & Xing Yang Research Groups

Significance

Surgery is an efficient way to treat localized prostate cancer (PCa), however, it is challenging to demarcate rapidly and accurately the tumor boundary intraoperatively, as existing tumor detection methods are seldom performed in real-time. To overcome those limitations, we develop a fluorescent molecular rotor that specifically targets the prostate-specific membrane antigen (PSMA), an established marker for PCa. The probes have picomolar affinity (IC₅₀= 63-118 pM) for PSMA and generate virtually instantaneous onset of robust fluorescent signal proportional to the concentration of the PSMA-probe complex. In vitro and ex vivo experiments using PCa cell lines and clinical samples, respectively, indicate the utility of the probe for biomedical applications, including real-time monitoring of endocytosis and tumor staging. Experiments performed in a PCa xenograft model reveal suitability of the probe for imaging applications in vivo.

Zhang, J., … Wang, Y., Bařinka, C. & Yang, X.: A prostate-specific membrane antigen activated molecular rotor for real-time fluorescence imaging,  Nature Comm. (2021)12:5460, https://doi.org/10.1038/s41467-021-25746-6