Solid-state NMR analysis of crosslinking in mussel protein glue.

Solid-state 13C and 15N NMR spectra have been obtained of intact adhesive plaques from the mussel Geukensia demissa labeled by L-[6-13C,6-15N]lysine. The plaques are rich in a polyphenolic protein glue which has 50 or more repeats of a nonapeptide sequence with one lysine per repeat. The average isotopic 15N enrichment of lysyl epsilon nitrogens in the plaques was 4%. These lysyl amines are not involved in ionic complexes and do not form observable concentrations of covalent crosslinks.