Specific chemical incorporation of L-DOPA and functionalized L-DOPA-hyaluronic acid in Candida antarctica lipase: creating potential mussel-inspired bioadhesives

Mussel adhesives proteins have been extensively studied as a promising alternative in bioadhesives due to their ability to provide durable anchoring under different surfaces in seawater. These charasteristics have been attributed to the presence of the reduced catechol form, 3,4-dihydroxyphenylalanine (DOPA) of its structure. However, its practical applications have been limited due to drawbacks with natural extraction. Here, a novel method have been described for site-specific chemical incorporation of L-3,4-dihydroxyphenylalanine methyl ester (L-DOPAME) into proteins, in particular Candida antartica fraction B (CAL-B) lipase. Two strategies were followed, direct conjugation of DOPA at the C-terminus on the surface of the protein, and protein conjugation with tailor-made glycopolymers (DOPA-hyaluronic acid (HA) polymers) at the N-terminus. In all cases, the characterization of the new DOPA-proteins was carried out using circular dichroism, fluorescence or mass spectrometry. An improvement in the activity (in some cases more than 2 times) or the thermostability of CAL-B (with a half live 4 fold greater in some cases) was found by the incorporation of DOPA molecules. These DOPA-proteins showed excellent underwater covalent adhesive ability on amino functionalized surfaces in aqueous media compared to other modified [e.g. tyrosine modified (TYR)] CAL-B proteins. At pH 8.5, CALB-DOPA proteins were completely adsorbed after 90 min of incubation, whereas about 10% of CALB-HA or CALB-TYR proteins were adsorbed at the same time. Native CAL-B adsorption was not observed. These results suggest a potential application of these DOPA-proteins as bioglues or bioadhesives for practical underwater applications.