Conformational Study of Silk-Like Peptides Containing the Calcium-Binding Sequence from Calbindin D9k Using 13C CP/MAS NMR Spectroscopy

Abstract

The calcium-binding sites of calbindin D(9k) have a helix-loop-helix motif. In this study, the helix motifs were replaced by several Ala-Gly repeating regions designed on the basis of the primary sequences of several silk fibroins. The synthesized peptides were treated with several organic solvents to modify the secondary structure of the Ala-Gly repeating regions. The local structures of the Ala-Gly repeating regions, as well as the calcium-binding motif, D(9k)-loop (D(9k)L), were determined by (13)C CP/MAS NMR spectroscopy. In the four peptides containing D(9k)L synthesized, the poly(Ala) domains retain the ability to undergo a conformational transition from alpha-helical to beta-sheet in (A)(12)-D(9k)L despite the presence of the D(9k)L domain at the center of the peptide molecule, but the presence of this domain in the other model peptides synthesized has a marked effect on the conformation of the added silk-like domains. The results showed that the structures of the Ala-Gly repeating regions can be controlled by the choice of both the organic solvent and the amino acid sequence of the Ala-Gly repeating regions without disrupting the secondary structure of D(9k)L suggesting that it may retain its ability to bind calcium ions.