Relationship between nuclear magnetic resonance chemical shift and protein secondary structure.

Syntheses and polymerizations of alpha-amino acid N-carboxyanhydrides (NCAs) were reported for the first time by Hermann Leuchs in 1906. Since that time, these cyclic and highly reactive amino acid derivatives were used for stepwise peptide syntheses but mainly for the formation of polypeptides by ring-opening polymerizations. This review summarizes the literature after 1985 and reports on new aspects of the polymerization processes, such as the formation of cyclic polypeptides or novel organometal catalysts. Polypeptides with various architectures, such as diblock, triblock, and multiblock sequences, and star-shaped or dendritic structures are also mentioned. Furthermore, lyotropic and thermotropic liquid-crystalline polypeptides will be discussed and the role of polypeptides as drugs or drug carriers are reviewed. Finally, the hypothetical role of NCAs in molecular evolution on the prebiotic Earth is discussed.

Polypeptides and 100 years of chemistry of alpha-amino acid N-carboxyanhydrides.

A survey of recent high-resolution solid-state 13C NMR studies is given to illustrate how and to what extent 13C chemical shifts of a variety of molecular systems are displaced upon conformational changes. Examples are taken from studies of alkanes, polysaccharides, polypeptides, and naturally occurring and synthetic ionophores, in which more than single conformations are available owing to either crystalline polymorphs or a variety of metal-ligand interactions. The magnitude of the conformation-dependent 13C chemical shifts are in many instances as large as 8 ppm and are well related to a set of torsion angles of nearby single bonds. The application of this concept to conformational characterization is also discussed.

Conformation‐dependent 13C chemical shifts: A new means of conformational characterization as obtained by high‐resolution solid‐state 13C NMR

Chemical Shift Tensor – the Heart of NMR: Insights into Biological Aspects of Proteins

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 (Wyckoff et 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), Oldfield et 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.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033583500004017

Protein structure by solid-state NMR spectroscopy.

Secondary structure of peptides. 3. Carbon-13 NMR cross polarization/magic angle spinning spectroscopic characterization of solid polypeptides

Benzylamine-, triethylamine-, and pyridine-initiated terpolymerizations of alanine N- carboxyanhydride (Ala-NCA), glycine N-carboxyanhydride (Gly-NCA), and valine N-carboxyanhydride (Val-NCA) were conducted in various solvents. The molar compositions of the resulting terpolypeptides were determined from 'H NMR spectra. Their sequences were analyzed by means of 15N NMR spectroscopy, and nearly random sequences were found in all cases. The secondary structure of the solid "as-polymerized samples was characterized by means of 13C NMR CP/MAS spectroscopy. The a-helixlP-sheet ratio was determined for all three amino acid units separately. In contrast to glycine a substantial fraction (up to 60%) of Val units assumes the a-helical conformation. The composition of the secondary structure partially changes upon reprecipitation. In contrast to the random terpolypeptides the two isomeric sequence polypeptides (Ala-Gly-Val), and (Gly-Ala-Val), exclusively possess the &sheet structure. However, in the block copolypeptide (Ala))- (Gly),-(Val), the (Ala)l blocks assume the a-helical conformation, whereas the (Gly), and (Val), blocks exclusively take on the p-sheet structure.

Secondary structure of peptides. 20. Primary-secondary structure relationships of Ala/Gly/Val copolypeptides

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Secondary structure of peptides. 3. Carbon-13 NMR cross polarization/magic angle spinning spectroscopic characterization of solid polypeptides

Secondary structure of peptides. 20. Primary-secondary structure relationships of Ala/Gly/Val copolypeptides