Structure and folding of glucagon-like peptide-1-(7-36)-amide in aqueous trifluoroethanol studied by NMR spectroscopy

The conformational changes of free, monomeric glucagon-like peptide-1-(7-36 -amide (GLP-1) in aqueous solution with increasing concentrations of 2,2,2- trifluoroethanol (TFE) were monitored by NMR spectroscopy. It was found tha t GLP-1 gradually assumes a stable, single-stranded helical structure in wa ter solution when the TFE concentration is increased from 0 to 35% (v/v). N o further structural changes were observed at higher TFE concentrations. Th e structure of GLP-1 in 35% TFE was determined from 292 distance restraints and 44 angle restraints by distance geometry, simulating annealing and res trained energy minimization. The helical structure extends from T7 to K28, with a less well-defined region around G16 and a disordered six-residue N-t erminal domain. The folding process of GLP-1 from random coil (in water) to helix (in 35% TFE) is initiated by the formation of the C-terminal segment of the helix that is extended gradually towards the N-terminus of the pept ide with increasing concentration of TFE. The exchange rates of the slow ex changing amide protons indicate that the C-terminal part of the helix is mo re stable than the N-terminal part. Copyright (C) 2001 John Wiley & Sons, L td.