On the location of β-turns

A review of oxygen-17 solid-state NMR of organic materials--towards biological applications

17O solid state NMR of organic materials is developing rapidly. This article provides a snapshot of the current state of development of this field. The NMR techniques and enrichment protocols that are driving this progress are outlined. The (17)O parameters derived from solid-state NMR experiments are summarized and the structural sensitivity of the approach to effects such as hydrogen bonding highlighted. The prospects and challenges for (17)O solid-state NMR of biomolecules are discussed.

Cyclic peptide substrates of pp60c-src. Synthesis and evaluation

To study the effects of constrained conformation and amino acid sequence on their kinetic parameters, a series of cyclic peptides were synthesized and each was tested as both a substrate and an inhibitor of pp60c-src, the product of the src proto-oncogene. The amino acid sequences were derived from Glu-Leu-Pro-Tyr-Ala-Gly and from the autophosphorylation site of pp60c-src (Ile-Glu-Asp-Asn-Glu-Tyr-Ala-Ala-Arg-Gln-Gly). Linear precursor peptides were synthesized by SPPS on aminomethylated polystyrene resin using the Fmoc-tert-butyl protection scheme with 4-hydroxymethyl-3-methoxyphenoxyacetic acid as the linkage agent. The peptides were cleaved from the support with 1% TFA in dichloromethane with the N-terminal Fmoc and the side-chain protecting groups in place. Removal of the Fmoc group with diethylamine and cyclization with BOP afforded cyclic peptides in 55-78% yield. Side-chain deprotection and further purification gave the final products in 25-48% yields based on their linear precursors. Based on the activities of the linear analogues, cyclization had little effect on the binding (Ki and Km) and rate of phosphorylation (Vmax) of cyclo(Glu-Leu-Pro-Tyr-Ala-Gly) and cyclo(Ile-Glu-Asp-Asn-Glu-Tyr-Ala-Ala-Arg-Gln). A series of cyclic decapeptides that contained the dipeptide D-Phe-Pro inserted in various positions in the autophosphorylation sequence showed marked differences in Ki, Km and Vmax. Compared to the well characterized linear substrate Val-5 angiotensin II, the D-Phe-Pro-containing cyclic peptides have higher Vmax values but differ little in Km, with values in the millimolar range.

17O n.m.r. studies of amino acids in the solid state, in single- and polycrystalline forms

A single crystal of 17O enriched alpha-glycine was grown by slow evaporation of aqueous solution. 17O n.m.r. studies of the alpha-glycine molecule in single crystalline form revealed five 17O transitions each consisting of two lines due to inequivalency of the oxygen atoms in the unit cell, with each of these lines revealing a dipolar interaction between the 17O and the nearest hydrogen atom. The spectral width was found to be of the order of magnitude of MHz and the linewidths of the order of magnitude of 2 kHz.