A Glycosylated Byssal Precursor Protein from the Green Mussel Perna viridis with Modified Dopa Side-chains

Abstract

Foot tissue of the green mussel Perna viridis contains a variety of byssal precursor proteins with the unusual redox-active amino acid, Dopa (L-β-3,4-dihydroxyphenyl-α-alanine). Eight proteins were detectable in acidic extracts of the Perna foot by a redox cycling assay with nitroblue tetrazolium. In one of these, however, P. viridis foot protein-1 (Pvfp-1), activity was not due to Dopa, but to another redox-active derivative. Based on specific colorimetric derivatization with Arnow's reagent, ninhydrin and phenylisothiocyanate (Edman), mass spectrometry, the redox-active derivative in Pvfp-1 is not consistent with any known modification. Another uncommon modification of Pvfp-1 involves O-glycosylation of threonine by mannose, glucose or fucose. As in previously characterized fp-1s, the primary sequence of the Pvfp-1 (apparent mass 89 kDa) has two consensus decapeptide motifs; one is APPKPX₁TAX₂K and the other is APPPAX₁TAX₂K, where P is Pro/Hyp, and X₁ and X₂ are difucosylated threonine and a redox sensitive derivative of tyrosine or Dopa, respectively. Of these two unusual residues, X₂ is unique to Pvfp-1, whereas O-glycosylated Thr has been previously detected in freshwater mussel fp-1. The sequence homology of Pvfp-1 with the common structural motifs of the fp-1 protein family strongly suggests that the Pvfp-1 functions as the byssal coating (lacquer) protein.

Keywords:

• P. viridis
• byssal precursor proteins
• Dopa
• Pvfp-1
• green mussel

Acknowledgements

This work was supported by Grants-in-aid for 21st Century COE Program and for Scientific Research (No 12450330, No 13556057, No 14750709) by the Ministry of Education, Culture, Sports, Science and Technology of Japan. JHW received support from the Biomaterials Program (NIDCR) of the National Institutes of Health.