Surface properties of mussel adhesive protein component films

Mussel adhesive protein (MAP) is the adhesive agent used by the blue sea mussel ( Mytilus edulis) to attach the animal to various underwater surfaces. It is composed of 75→85 repeating decameric units with the reported primary sequence NH 2-A(1)-K(2)-P(3)-S(4)-Y(5)-Hyp(6)-Hyp(7)-T(8)-DOPA(9)-K(10)-COOH. This study identifies and compares the surface properties of the decameric unit, selected fragments and individual amino acid constituents with the complete MAP preparation. These molecular systems were examined: (a) in the solid state as thin films formed on germanium substrata using multiple-attenuated-internal-reflectance infrared (MAIR-IR) spectroscopy, ellipsometry and contact angle analysis; and (b) in the solution state using circular dichroism (CD) spectroscopy. Extensive molecular modelling of the decamer was performed making integral use of the experimentally derived data. These cumulative semi-empirical and empirical results suggest a conformation for the decamer that closely associates the l-DOPA and tyrosine residues with the solid substratum. This model provides the first representation of MAP derived from a rational integration of theoretical and experimental data. On the basis of this model, a possible explanation for the bioadhesive properties of MAP is suggested.