Macromolecules, Vol.51, No.17, 6746-6756, 2018
Dynamics of Alanine Methyl Groups in Alanine Oligopeptides and Spider Dragline Silks with Different Packing Structures As Studied by C-13 Solid-State NMR Relaxation
The dynamics of alanine methyl groups in alanine and polyalanine regions in Nephila clavata dragline and recombinant silks changed remarkably depending on the different packing arrangements. In particular, a notable difference in the C-13 spin-lattice relaxation time T(1 )of Ala C beta peaks was observed in the solid-state NMR between (Ala)(6 )and (Ala)(7), which have rectangular and staggered packing arrangements, respectively. Moreover, the remarkably longer T-1 value of the lowest field peak in Ala C beta carbons clearly indicated the presence of staggered packing structure. Then, the relaxation behavior of polyalanine regions in spider dragline silks with mixed packing arrangements were clarified in both dry and hydrated states. The partial appearance of the staggered packing structure in (Ala)(6) with rectangular packing structure was detected from the changes in line shapes of Ala( 13)C beta peaks for the three kinds of(13)C single-labeled (Ala)(6 )samples together with the change in their relaxation behavior.