Hydrophobic oligopeptides in solution and in phospholipid vesicles: synthetic fragments of bacteriorhodopsin

pH effects on the conformational preferences of amyloid beta-peptide (1-40) in HFIP aqueous solution by NMR spectroscopy

The structure and aggregation state of amyloid beta-peptide (Abeta) in membrane-like environments are important determinants of pathological events in Alzheimer's disease. In fact, the neurotoxic nature of amyloid-forming peptides and proteins is associated with specific conformational transitions proximal to the membrane. Under certain conditions, the Abeta peptide undergoes a conformational change that brings the peptide in solution to a "competent state" for aggregation. Conversion can be obtained at medium pH (5.0-6.0), and in vivo this appears to take place in the endocytic pathway. The combined use of (1)H NMR spectroscopy and molecular dynamics-simulated annealing calculations in aqueous hexafluoroisopropanol simulating the membrane environment, at different pH conditions, enabled us to get some insights into the aggregation process of Abeta, confirming our previous hypotheses of a relationship between conformational flexibility and aggregation propensity. The conformational space of the peptide was explored by means of an innovative use of principal component analysis as applied to residue-by-residue root-mean-square deviations values from a reference structure. This procedure allowed us to identify the aggregation-prone regions of the peptide.

Characterization of the mobility of various chemical groups in the purple membrane of Halobacterium halobium by 13C, 31P and 2H solid state NMR

Lyophilized purple membrane sheets have been investigated by C-13- and P-31-cross polarization/magic angle spinning NMR spectroscopy. The high-resolution C-13 spectrum and its non-quaternary suppression version indicate fast protein side-chain motions but a rigid backbone structure on a time scale of roughly less than 0.001 to 0.01 s. Three components of exchangeable hydrogen have been detected by deuterium NMR. The mean exchange time of the peptide hydrogens must be longer than 1 microsecond. The medium component is attributed to mobile side-chains. In addition a narrow line has been observed which is assigned to the residual hydration water.