PRESENCE OF PHOSPHORUS IN NEPHILA-CLAVIPES DRAGLINE SILK

Solid-state P-31-NMR of Nephila clavipes dragline silk indicates the p resence of phosphorus in at least two chemically distinct environments . Amino acid analyses of acid-hydrolyzed silk confirm the presence of phosphotyrosine as one of the phosphorus-containing components. The un usual chemical shift (18.9 ppm downfield from 85% H3PO4), proton chemi cal shift, and acid lability of a second component suggest that it is par? of a strained five-membered cyclic phosphate that might be found on a beta-D-ribose. The five-membered cyclic phosphate is not removed from the silk fibers by exhaustive aqueous extraction, It is absent in nascent silk fibroin from the glands, suggesting that its formation i s part of the fiber processing that occurs in the ducts leading to the spinnerets. High-resolution NMR spectra of silk dissolved in propioni c acid/12 N HCl (50:50 v/v) show five phosphorus sites assigned to pho sphorylated tyrosine residues, phosphorylated serine residues, inorgan ic phosphate, and two hydrolysis products of the cyclic phosphate comp ound. The observed posttranslational phosphorylation may be important in the processing and modulation of the physical properties of draglin e silk.