Beta -pleated sheet strands

A. a triple-stranded extended helix B. a beta-pleated sheet... 

FIGURE 19.10 Beta-pleated sheet protein structure The /3-pleated sheet is maintained by interactions between the peptide backbones of neighboring protein strands. 

From WAXS and SAED data of both ProNectin F lyophilized powder and sprayed fibrils, the current model indicates that ProNectin F crystallizes into a chain folded pleated sheet of beta strands (Anderson et a/. 1994). The strands are oriented antiparallel. The beta strands are not fully extended, but have a more compressed crankshaft conformation. This conformation agrees with the predicted conformation of unoriented silk fibroin protein, the Silk I structure (Lotz and Keith 1971). The crystal dimension in the c direction (along the peptide backbone) is consistent with a theoretical length of 11.6 nm for nine SEP blocks (54 amino acids) in this conformation. This predicts that the width of the ProNectin F tile is controlled at least in part by the number of amino acids in the silklike block domains. 

---