Lynn W. Jelinski

Molecular orientation and two-component nature of the crystalline fraction of spider dragline silk.

The molecular origin of the exceptional mechanical properties of spider silk is unclear. This paper presents solid-state 2H nuclear magnetic resonance data from unoriented, oriented, and supercontracted fibers, indicating that the crystalline fraction of dragline silk consists of two types of alanine-rich regions, one that is highly oriented and one that is poorly oriented and less densely packed. A new model for the molecular-level structure of individual silk molecules and their arrangement in the fibers is proposed. These data suggest that it will be necessary to control the secondary structure of individual polymer molecules in order to obtain optimum properties in bio-inspired polymers.

Orientation, structure, wet-spinning, and molecular basis for supercontraction of spider dragline silk

This manuscript reviews work from our laboratory that addresses the orientation, secondary structure, wet-spinning, and molecular basis for supercontraction of spider silk. It identifies the poly(alanine) runs as the crystalline regions, establishes the degree of orientation of these regions, and identifies the secondary structural elements of the conserved L-G-X-Q (X = G, S, or N) regions. It also describes methods for spinning very small amounts of protein polymers and it sets forth several molecular-level hypotheses concerning supercontraction.

Rotational-echo Double-resonance in Complex Biopolymers: a Study of Nephila Clavipes Dragline Silk

Rotational-Echo Double-Resonance (REDOR) NMR on strategically 13C and 15N labeled samples is used to study the conformation of the LGXQ (X = S, G, or N) motif in the major ampullate gland dragline silk from the spider Nephila clavipes. A method is described for calculating REDOR dephasing curves suitable for background subtractions, using probability distributions of nitrogen atoms surrounding a given carbon site, which are developed from coordinates in the Brookhaven Protein Data Bank. The validity of the method is established by comparison to dephasings observed from natural abundance 13C peaks for G and A. Straightforward fitting of universal REDOR dephasing curves to the background corrected peaks of interest provide results which are not self-consistent, and a more sophisticated analysis is developed which better accounts for 15N labels which have scrambled from the intended positions. While there is likely some heterogeneity in the structures formed by the LGXQ sequences, the data indicate that they all form compact turn-like structures.

Presence of phosphorus in Nephila clavipes dragline silk

Solid-state 31P-NMR of Nephila clavipes dragline silk indicates the presence of phosphorus in at least two chemically distinct environments. Amino acid analyses of acid-hydrolyzed silk confirm the presence of phosphotyrosine as one of the phosphorus-containing components. The unusual chemical shift (18.9 ppm downfield from 85% H3PO4), proton chemical shift, and acid lability of a second component suggest that it is part of a strained five-membered cyclic phosphate that might be found on a beta-D-ribose. The five-membered cyclic phosphate is not removed from the silk fibers by exhaustive aqueous extraction. It is absent in nascent silk fibroin from the glands, suggesting that its formation is part of the fiber processing that occurs in the ducts leading to the spinnerets. High-resolution NMR spectra of silk dissolved in propionic acid/12 N HCl (50:50 v/v) show five phosphorus sites assigned to phosphorylated tyrosine residues, phosphorylated serine residues, inorganic phosphate, and two hydrolysis products of the cyclic phosphate compound. The observed posttranslational phosphorylation may be important in the processing and modulation of the physical properties of dragline silk.

High-Resolution NMR of Solids

This chapter is intended to provide a bridge between the principles of NMR spectroscopy of solids and the practical execution of these experiments in the laboratory. The point of view is one of physical concepts, rather than of mathematical rigor. Interwoven with the fundamentals of solid-state NMR are practical tips garnered from laboratory experience. The presentation of material is intended to apply generally to both superconducting and electromagnet geometries. Standard experiments are emphasized, rather than the more exotic and instrument-demanding techniques. The introduction contrasts the nuclear-spin interactions (Zeeman, dipole–dipole, scalar, chemical shift) in solution and in the solid state. The section on magic-angle spinning examines the effects of mechanical specimen rotation on these nuclear-spin interactions. The concept of dipolar decoupling is introduced next, followed by a section on cross-polarization. Some of the more standard solid-state NMR experiments are described in the section on advanced techniques. Finally, the section on instrumental considerations presents spectrometer and probe requirements for solid-state NMR operation.

Two novel solid‐state nuclear magnetic resonance probes

The design and construction of two novel solid‐state NMR probes are described. One probe incorporates a high‐resolution goniometer for single‐crystal studies, while the other can apply tension (≳5000 N) to fiber bundles. Deuterium spectra demonstrating the sensitivity of both probes are presented.

Solid State NMR and its Applications to Biomedical Research

Publisher Summary Multidimensional nuclear magnetic resonance (NMR) has proven to be a valuable tool for establishing the structure and dynamics of biological molecules in solution. Solution NMR is frequently combined with X-ray diffraction and molecular mechanics calculations to determine the extent to which solution properties are retained in the solid state. However, many biological molecules cannot be prepared as single crystals. In addition, the presence of solvent may have a profound effect on the structure and dynamics of individual molecules, and change the nature of intermolecular interactions. Solution techniques are not adequate for the examination of molecules or assemblies of molecules in which motion is restricted, so that isotropic tumbling fast on the NMR time scale does not occur. Techniques applied to study solid samples of Synthetic polymers and inorganic glasses can be applied to questions of biological interest. This chapter outlines the differences between nuclear interactions in solution and in the solid state, and then introduces the techniques commonly used to obtain useful spectra from solid samples. A number of applications are presented in which information uniquely available from solid-state NMR has increased our understanding of a biological material or process. The wide scope of this chapter precludes a complete listing of all related research.

NMR Imaging: Introduction and Survey

The basic principles governing how magnetic field gradients are used for NMR imaging (and flow measurements) are introduction. Topics covered include slice selection, phase encoding, frequency encoding, factors determining spatial revolution, T1 and T2 effects and chemical shift effects, and determining flow velocity and diffusion information.