A DECODER NMR study of backbone orientation in Nephila clavipes dragline silk under varying strain and draw rate

Using DECODER (direction exchange with correlation for orientation distribution evaluation and reconstruction) NMR, we probe the orientations of carbonyl carbons in [1-C-13]glycine-labeled dragline silk under conditions of varying strain and fiber draw rate. A model-specific reconstruction of the molecular orientation distribution incorporating beta sheets and polyglycine II helices indicates that the structures' alignment along the fiber can be described by a pair of Gaussian distributions with full width at half-maxima of 20 and 68degrees and similar to45 and similar to55% relative contributions to the signal intensity. The alignment along the fiber was found to change appreciably when the drawing tension on the fiber was relaxed in a sample drawn at 4 cm/s while little change was observed in a sample drawn at 2 cm/s. The degree of alignment along the fiber was found to increase with fiber draw rate.