Solid-state NMR comparison of various spiders' dragline silk fiber

Major ampullate (dragline) spider silk is a coveted biopolymer due to its combination of strength and extensibility. The dragline silk of different spiders have distinct mechanical properties that can be qualitatively correlated to the protein sequence. This study uses amino acid analysis and carbon-13 solid-state NMR to compare the molecular composition, structure, and dynamics of major ampullate dragline silk of four orb-web spider species ( Nephila clavipes , Araneus gemmoides , Argiope aurantia , and Argiope argentata ) and one cobweb species ( Latrodectus hesperus ). The mobility of the protein backbone and amino acid side chains in water exposed silk fibers is shown to correlate to the proline content. This implies that regions of major ampullate spidroin 2 protein, which is the only dragline silk protein with any significant proline content, become significantly hydrated in dragline spider silk.

Solid-state NMR investigation of major and minor ampullate spider silk in the native and hydrated states

Silks spun from the major (Ma) and minor (Mi) ampullate glands by the spider Nephila clavipes respond to water differently. Specifically, Ma silk supercontracts (shrinks 40-50% in length) while Mi silk does not contract at all when hydrated with water. In the present study, 1H --> 13C cross polarization magic angle spinning (CP-MAS), 13C MAS NMR collected with dipolar decoupling, and two-dimensional wide-line separation spectra are presented on Mi silk in its native and hydrated state and comparisons are made to Ma silk. This combination of NMR data demonstrates that water plasticizes Mi and Ma silk similarly, with an increase in chain dynamics observed in regions containing Gly, Glu, Ser, Tyr, Leu, and a fraction of Ala when the Mi silk is hydrated. Resonances that correspond to the poly(Ala) and poly(Gly Ala) motifs of Ma and Mi silk are predominately rigid indicating that water does not penetrate these beta-sheet domains.

NMR studies on fully hydrated membrane proteins, with emphasis on bacteriorhodopsin as a typical and prototype membrane protein

The 3D structures or dynamic feature of fully hydrated membrane proteins are very important at ambient temperature, in relation to understanding their biological activities, although their data, especially from the flexible portions such as surface regions, are unavailable from X-ray diffraction or cryoelectron microscope at low temperature. In contrast, high-resolution solid-state NMR spectroscopy has proved to be a very convenient alternative means to be able to reveal their dynamic structures. To clarify this problem, we describe here how we are able to reveal such structures and dynamic features, based on intrinsic probes from high-resolution solid-state NMR studies on bacteriorhodopsin (bR) as a typical membrane protein in 2D crystal, regenerated preparation in lipid bilayer and detergents. It turned out that their dynamic features are substantially altered upon their environments where bR is present. We further review NMR applications to study structure and dynamics of a variety of membrane proteins, including sensory rhodopsin, rhodopsin, photoreaction centers, diacylglycerol kinases, etc.

A study of conformational stability of polyglycine and poly(L-alanine), and polyglycine/poly(L-alanine) blends in the solid state by (13)C cross-polarization/magic angle spinning NMR

13C Cross-Polarization/Magic Angle Spinning nmr and T(1rhoH) experiments of polyglycine (PG), poly(L-alanine) (PLA), and PG/PLA blends prepared from dichloroacetic acid solution have been carried out, in order to elucidate the conformational stability of these polypeptides in the solid state. From these experimental results, it was clarified that the conformations of PG and PLA in their blends are strongly influenced by intermolecular hydrogen-bonding interactions that cause their miscibility at the molecular level.

A high-resolution solid-state 13C-NMR study on [1-13C]Ala and [3-13C]Ala and [1-13C]Leu and Val-labelled bacteriorhodopsin. Conformation and dynamics of transmembrane helices, loops and termini, and hydration-induced conformational change

We have recorded 100.7-MHz high-resolution solid-state 13C-NMR spectra of [3-13C]Ala, [1-13C]Ala-labelled, Leu-labelled and Val-labelled bacteriorhodopsin (bR), to analyze the conformation and dynamics of transmembrane alpha helices and hydration-induced conformational changes. We assigned the 13C-NMR signals of these 13C-labelled amino acid residues to portions of the transmembrane alpha helices, loops and N-terminus and C-terminus, based on the conformation-dependent 13C chemical shift. The assignment of peaks to the transmembrane alpha helices is straightforward in view of the characteristic 13C chemical shifts of the C beta and carbonyl carbons, referred to the data of the model system. The signals of the transmembrane alpha helices were further divided into three or four peaks which are ascribed to either a dispersion of torsion angles of the alpha helices or variation of environments around the helices. In addition, we found that conformation of the N-terminus and C-terminus of bR is virtually the random-coil form which undergoes rapid reorientational motion in the hydrated system. Further, we show that the higher-order (secondary and/or tertiary) structure of bR is influenced by the hydration/dehydration process of the purple membrane, as viewed from the peak profile of the Ala C beta 13C signals. This change of structure occurs between relative humidities of 2% and 4%, consistent with the shift of the absorption maxima of retinal, which arise from the protonation/deprotonation processes of the Schiff base. In contrast, no such change of the carbonyl signals occurs for the Leu, Val and Ala residues. For the latter two residues, some spectral changes were noted at the stage of full hydration.

Hydration effects on dynamics of polyglycine and sodium poly(L-glutamate)

Solid state nmr methods were applied to the study of the motions and structural heterogeneity in polyglycine, sodium poly(L-glutamate), and poly(L-alanine). The response of both the main-chain and side-chain resonances to the addition of water was studied using static and magic-angle sample-spinning line shapes as well as the carbon spin-lattice relaxation times, the proton spin-lattice relaxation time in the rotating frame, and the proton-carbon cross-polarization time. The polyglycine motions are not drastically affected by the addition of water when the polymer is in the 3(1)-helix or the beta-sheet structure. The sodium poly(L-glutamate), however, responds to increased hydration with little motion in the main-chain carbon atoms, but considerable flexibility of the side-chain atoms. The greatest motions are reported for the C5 carbon with rotational amplitudes about the C4-C5 bond of about of 50 degrees. In addition, motions somewhat less than half this size are required closer to the main chain.

Protein structure by solid-state NMR spectroscopy

The three-dimensional structures of proteins are among the most valuable contributions of biophysics to the understanding of biological systems (Dickerson & Geis, 1969; Creighton, 1983). Protein structures are utilized in the description and interpretation of a wide variety of biological phenomena, including genetic regulation, enzyme mechanisms, antibody recognition, cellular energetics, and macroscopic mechanical and structural properties of molecular assemblies. Virtually all of the information currently available about the structures of proteins at atomic resolution has been obtained from diffraction studies of single crystals of proteins (Wyckoffet al, 1985). However, recently developed NMR methods are capable of determining the structures of proteins and are now being applied to a variety of systems, including proteins in solution and other non-crystalline environments that are not amenable for X-ray diffraction studies. Solid-state NMR methods are useful for proteins that undergo limited overall reorientation by virtue of their being in the crystalline solid state or integral parts of supramolecular structures that do not reorient rapidly in solution. For reviews of applications of solid-state NMR spectroscopy to biological systems see Torchia and VanderHart (1979), Griffin (1981), Oldfieldet al. (1982), Opella (1982), Torchia (1982), Gauesh (1984), Torchia (1984) and Opella (1986). This review describes how solid-state NMR can be used to obtain structural information about proteins. Methods applicable to samples with macroscopic orientation are emphasized.