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 co nformation in dilute solution. Sedimentation equilibrium in the analyt ical ultracentrifuge of a dilute solution of protein (0.4 mg/mL) in ac etate buffer at pH 4.5 and I = 0.10 M yielded an apparent molecular we ight (whole distribution weight average, M-w,M-app) of 114 000 +/- 500 0 via the ''M'' procedure, a value in almost exact agreement with the monomeric molecular weight obtained by MALDI mass spectrometry. At th is low concentration, it is reasonable to assume thermodynamic idealit y, i.e., M-w,M-app similar to M-w. This result, together with plots of point weight average apparent molecular weight versus concentration f or three different loading concentrations (0.4, 0.8, 1.0 mg/mL), clear ly demonstrates that this protein is essentially monomeric in dilute s olution. 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 interpreta tion of this, in terms of an extended rather than globular conformatio n for the structure of mefp-1 in dilute solution, is considered, withi n plausible limits of molecular hydration, and models for the structur e in solution are considered, in light of the thermodynamic nonidealit y behavior of these molecules and previously published circular dichro ism data. The significance of these observations in terms of the bioad hesive properties of mefp-1 is described, and the very strong interact ion in dilute solution with a mucin glycoprotein is demonstrated.