Structural analysis of amyloid (beta) peptide fragment (25-35) in different microenvironments

Amyloid (beta) (A(beta)) peptides are one of the classes of amphiphilic molecules that on dissolution in aqueous solvents undergo interesting conformational transitions. These conformational changes are known to be associated with their neuronal toxicity. The mechanism of structural transition involved in the monomeric A(beta) to toxic assemblage is yet to be understood at the molecular level. Early results indicate that oriented molecular crowding has a profound effect on their assemblage formation. In this work, we have studied how different microenvironments affect the conformational transitions of one of the active amyloid (beta)-peptide fragments (A(beta)25-35). Spectroscopic techniques such as CD and Fourier transform infrared spectroscopy were used. It was observed that a stored peptide concentrates on dissolution in methanol adopts a minor (alpha)-helical conformation along with unordered structures. On changing the methanol concentration in the solvated film form, the conformation switches to the antiparallel (beta)-sheet structure on the hydrophilic surface, whereas the peptide shows transition from a mixture of helix and unordered structure into predominantly a (beta)-sheet with minor contribution of helix structure on the hydrophobic surface. Our present investigations indicate that the conformations induced by the different surfaces dictate the gross conformational preference of the peptide concentrate.