The importance of sulphur cross-links and hydrophobic interactions in the polymerization of barnacle cement

Solidified adhesive (cement) of three balanid barnacles (Crustacea: Cirripedia) was dissolved using different concentrations of sodium dodecyl sulphate containing a reducing agent. The proteins were separated using SDS-PAGE and blotted onto polyvinylidene difluoride membrane for sequencing. Commonly occurring bands in the cement of each species were identified. One particular protein of 39 kD, found in the cement of Balanus perforatus , has the following N-terminal sequence: TYFPVLSYG?SSSLAPVI, where the? is most likely cysteine. Quinones were not identified in the cement by either infra-red, ultraviolet-visible or solid-state nuclear magnetic resonance spectroscopy and the successful dissolution and sequencing of cement proteins mitigates against their presence. Cement contains a mixture of highly hydrophobic proteins which are cross-linked through cysteine residues. It is the combination of these two components which makes cement highly resistant to chemical degradation. As a result bacteria are usually absent from the cement, possibly further excluded from the porous core of the cement by its smooth outer crust.