Klara Osapay

Analysis of proton chemical shifts in regular secondary structure of proteins.

SummaryThe contribution of peptide groups to Hα and Hβ proton chemical shifts can be modeled with empirical equations that represent magnetic anisotropy and electrostatic interactions [Ösapay, K. and Case, D.A. (1991) J. Am. Chem. Soc., 113, 9436–9444]. Using these, a model for the ‘random coil’ reference state can be generated by averaging a dipeptide over energetically allowed regions of torsion-angle space. Such calculations support the notion that the empirical constant used in earlier studies arises from neighboring peptide contributions in the reference state, and suggest that special values be used for glycine and proline residues, which differ significantly from other residues in their allowed ϕ,ψ-ranges. New constants for these residues are reported that provide significant improvements in predicted backbone shifts. To illustrate how secondary structure affects backbone chemical shifts we report calculations on oligopeptide models for helices, sheets and turns. In addition to suggesting a physical mechanism for the widely recognized average difference between α and β secondary structures, these models suggest several additional regularities that should be expected: (a) Hα protons at the edges of β-sheets will have a two-residue periodicity; (b) the Hα2 and Hα3 protons of glycine residues will exhibit different shifts, particularly in sheets; (c) Hβ protons will also be sensitive to local secondary structure, but in different directions and to a smaller extent than Hα protons; (d) Hα protons in turns will generally be shifted upfield, except those in position 3 of type I turns. Examples of observed shift patterns in several proteins illustrate the application of these ideas.

Therapeutic applications of somatostatin analogues

The neuropeptide somatostatin is widely expressed both in the periphery and in the central nervous system (CNS) and has multiple functions: it regulates endocrine and exocrine secretion, it possesses antiproliferative properties and it acts as a neurotransmitter/neuromodulator. These diverse physiological effects are mediated by a family of G-protein-coupled cell surface receptors, the somatostatin receptors, named sst1 through sst5. Short synthetic somatostatin analogues (octreotide, lanreotide) that are in clinical use (e.g., for cancer therapy, gastrointestinal disorders) primarily interact with sst2. Somatostatin analogues with selective receptor binding can be useful in the treatment of gastrointestinal, cardiovascular, endocrine, immunological or CNS diseases such as epilepsy and Alzheimer’s disease. This paper reviews selected somatostatin related publications and patents issued between 1995 and 1998 for new drug candidates and their possible therapeutic applications.