13C solid-state NMR study of the 13C-labeled peptide, (E)8GGLGGQGAG(A)6GGAGQGGYGG as a model for the local structure of Nephila clavipes dragline silk (MaSp1) before and after spinning

We prepared the water soluble model peptide, (E)8GGLGGQGAG(A)6GGAGQGGYGG, to throw light on the local structure of spidroin 1 (MaSpl) protein in spider dragline silk of Nephila clavipes before and after spinning. Solution 13C NMR showed that the conformation of the peptide in aqueous solution was essentially random coil. Solid-state NMR was used to follow conformation-dependent 13C chemical shifts in 13C selectively labeled versions of the peptide. The peptide lyophilized from an aqueous solution at neutral pH (hereafter referred to as without acid treatment)was used to mimic the state of the spidroin stored in the spider's silk gland while the peptide precipitated from the acidic solution (with acid treatment) was used to simulate the role of acid treatment in inducing conformation change in the natural spinning process. In without acid treatment, the fraction of random coil conformation was lowest in the N-terminal region (residues 1518) when compared with the C-terminus. The conformational change produced by the acid treatment occurred in the sequence, G15AG(A)6GGAG27, interposed between pairs of Gly residues pairs, Gly12,13, and Gly29,30. The acid treated peptide showed a remarkable decrease in the fraction of random coil conformation from A20 to A23 in the poly-Ala region when compared with the peptide without acid treatment. These observations taken together suggest that the peptide can be used as a model for studying the localization of the conformation change in spider silk fibroin in the natural spinning and the role of acid treatment in this process. (C) 2011 Wiley Periodicals, Inc. Biopolymers 97: 347354, 2012.