The degree of aggregation in solution controls the adsorbed amount of mussel adhesive proteins on a hydrophilic surface

The adsorption behaviour of the mussel adhesive protein Mefp-1 on a hydroph ilic surface was studied by Surface Plasmon Resonance (SPR) at pH values of 4.5 and 6.5 under aerobic conditions and at an ion strength of 0.1 M NaCl. In this environment Mefp-1 molecules aggregate by crosslinking, likely via Dopa-Dopa quinone charge transfer interactions. The initial rate of aggreg ation increases with increasing pH, as could be derived from Photon Correla tion Spectroscopy measurements. The degree of aggregation deter-mines the a dsorption plateau value of Mefp-1. Step-like adsorption curves have been fo und at pH 6.5, as well as at pH 4.5, which can be interpreted as the adsorp tion of an ad-layer of Mefp-1 aggregates onto the initially adsorbed Mefp-1 layer on the surface. The rate of formation of this second layer increases with increasing pH and Mefp-1 concentration. The affinity of the ad-layer for the first adsorbed layer appears to be much smaller than the affinity o f the first layer for the surface (Poly Vinyl Alcohol). Probably, also the ad-layer formation proceeds by the establishment of specific crosslinks wit h the first layer of adsorbed Mefp-1. (C) 2001 Elsevier Science B.V. All ri ghts reserved.