Design Parameters of Tissue-Engineering Scaffolds at the Atomic Scale

Stem-cell behavior is regulated by the material properties of the surrounding extracellular matrix, which has important implications for the design of tissue-engineering scaffolds. However, our understanding of the material properties of stem-cell scaffolds is limited to nanoscopic-to-macroscopic length scales. Herein, a solid-state NMR approach is presented that provides atomic-scale information on complex stem-cell substrates at near physiological conditions and at natural isotope abundance. Using self-assembled peptidic scaffolds designed for nervous-tissue regeneration, we show at atomic scale how scaffold-assembly degree, mechanics, and homogeneity correlate with favorable stem cell behavior. Integration of solid-state NMR data with molecular dynamics simulations reveals a highly ordered fibrillar structure as the most favorable stem-cell scaffold. This could improve the design of tissue-engineering scaffolds and other self-assembled biomaterials.

Towards the Native Binding Modes of Antibiotics that Target Lipid II

The alarming rise of antimicrobial resistance (AMR) imposes severe burdens on healthcare systems and the economy worldwide, urgently calling for the development of new antibiotics. Antimicrobial peptides could be ideal templates for next-generation antibiotics, due to their low propensity to cause resistance. An especially promising branch of antimicrobial peptides target lipid II, the precursor of the bacterial peptidoglycan network. To develop these peptides into clinically applicable compounds, detailed information on their pharmacologically relevant modes of action is of critical importance. Here we review the binding modes of a selection of peptides that target lipid II and highlight shortcomings in our molecular understanding that, at least partly, relate to the widespread use of artificial membrane mimics for structural studies of membrane-active antibiotics. In particular, with the example of the antimicrobial peptide nisin, we showcase how the native cellular membrane environment can be critical for understanding of the physiologically relevant binding mode.

Bacteriophage Tail-Tube Assembly Studied by Proton-Detected 4D Solid-State NMR

Obtaining unambiguous resonance assignments remains a major bottleneck in solid-state NMR studies of protein structure and dynamics. Particularly for supramolecular assemblies with large subunits (>150 residues), the analysis of crowded spectral data presents a challenge, even if three-dimensional (3D) spectra are used. Here, we present a proton-detected 4D solid-state NMR assignment procedure that is tailored for large assemblies. The key to recording 4D spectra with three indirect carbon or nitrogen dimensions with their inherently large chemical shift dispersion lies in the use of sparse non-uniform sampling (as low as 2 %). As a proof of principle, we acquired 4D (H)COCANH, (H)CACONH, and (H)CBCANH spectra of the 20 kDa bacteriophage tail-tube protein gp17.1 in a total time of two and a half weeks. These spectra were sufficient to obtain complete resonance assignments in a straightforward manner without use of previous solution NMR data.