Bulk adhesive strength of recombinant hybrid mussel adhesive protein

Mussel adhesive proteins (MAPs) have received increased attention as potential biomedical and environmental friendly adhesives. However, practical application of MAPs has been severely limited by uneconomical extraction and unsuccessful genetic production. Developing new adhesives requires access to large quantities of material and demonstrations of bulk mechanical properties. Previously, the authors designed fp-151, a fusion protein comprised of six MAP type 1 (fp-1) decapeptide repeats at each MAP type 5 (fp-5) terminus and successfully expressed it in Escherichia coli. This recombinant hybrid protein exhibited high-level expression, a simple purification and high biocompatibility as well as strong adhesive ability on a micro-scale. In the present work, investigations on the bulk adhesive properties of semi-purified ( approximately 90% purity) fusion fp-151 were performed in air. The unmodified recombinant fp-151, as expressed, contains tyrosine residues and showed significant shear-adhesive forces ( approximately 0.33 MPa). Adhesion strength increased ( approximately 0.45 MPa) after enzymatic oxidation of tyrosine residues to l-3,4-dihydroxyphenylalanine (DOPA) groups. Addition of cross-linkers such as iron(III), manganese(III) and periodate (IO(4)(-)) generally enhanced adhesion, although too much addition decreased adhesion. Among the three cross-linking reagents examined, the non-metallic oxidant periodate showed the highest shear-adhesive forces ( approximately 0.86 MPa). In addition, it was found that adhesive strengths could be increased by adding weights to the samples. The highest adhesion strength found was that of DOPA-containing fp-151 cross-linked with periodate and having weights applied to the samples ( approximately 1.06 MPa). Taken together, the first bulk-scale adhesive force measurements are presented for an expressed recombinant hybrid mussel adhesive protein.