Abstract
Silkmoth proteins secreted from the follicular cells that surround the oocyte form a large extracellular assembly which is important for protecting and sustaining the structure of the oocyte and the developing embryo. These proteins have been classified into two major families (A and B). Sequence analysis showed conservation of a central domain containing long stretches of six amino acid residue repeats in both families, which have been suggested to be organized in Ξ²βsheet structures. In this work NMR and CD spectra, as well as molecular calculations, have been used to investigate the conformational properties of two synthetic peptides (A and B), analogues of parts of the central domain of silkmoth chorion proteins of the A and B families, respectively. These peptides consist of three tandem repeats of the sixβresidue basic motif. Analysis of CD spectra of the two peptides in aqueous solutions and mixtures with organic solvents revealed Ξ²βsheet and turn structural elements with a percentage higher than 40%. NOESY spectra at low temperatures (263β273 K) show sequential nOe connectivities (i, i+1), indicative of a relative flexibility. The presence of H N~i~βHN~i+1~ crossβpeaks and medium HΞ±~i~βHN~i+1~ connectivities, chemical shift deviations and temperature coefficient data provide, for the first time, experimental evidence that local folded structures around Gly residues occur in peptide segments of chorion proteins in solution. Simulated annealing calculations were used to examine the conformational space of the peptides and to probe the initial steps of amyloid fibril formation in the case of chorion proteins. Copyright Β© 2004 European Peptide Society and John Wiley & Sons, Ltd.