Structure and mucoadhesion of mussel glue protein in dilute solution

Purified mussel adhesive protein mefp-1 (Mytilus edulis foot protein 1) has been studied regarding its state of oligomerization and gross conformation in dilute solution. Sedimentation equilibrium in the analytical ultracentrifuge of a dilute solution of protein (0.4 mg/mL) in acetate buffer at pH 4.5 and I = 0.10 M yielded an apparent molecular weight (whole distribution weight average, M-w,M-app) of 114 000 +/- 5000 via the "M*" procedure, a value in almost exact agreement with the monomeric molecular weight obtained by MALDI mass spectrometry. At this low concentration, it is reasonable to assume thermodynamic ideality, i.e., M-w,M-app similar to M-w. This result, together with plots of point weight average apparent molecular weight versus concentration for three different loading concentrations (0.4, 0.8, 1.0 mg/mL), clearly demonstrates that this protein is essentially monomeric in dilute solution. Sedimentation velocity experiments yielded an estimate of the sedimentation coefficient s(20,w)(0) = 2.34 +/- 0.17 S, which for M = 110 000 gives a frictional ratio f/f(0) = 3.2 +/- 0.3. The interpretation of this, in terms of an extended rather than globular conformation for the structure of mefp-1 in dilute solution, is considered, within plausible limits of molecular hydration, and models for the structure in solution are considered, in light of the thermodynamic nonideality behavior of these molecules and previously published circular dichroism data. The significance of these observations in terms of the bioadhesive properties of mefp-1 is described, and the very strong interaction in dilute solution with a mucin glycoprotein is demonstrated.