Protease-catalyzed synthesis of oligo(l-aspartic acid) and its use for bioadhesives

Abstract

Poly(aspartic acid) is a biodegradable water-soluble polymer. It has been studied as an alternative to traditional anionic water-soluble polymers such as poly(acrylic acid). It also has potential uses in scaffolding for tissue growth, artificial skin, drug delivery and other biomedical applications. In our group, oligo(-ethyl-aspartate) was synthesized by a green, efficient and cost-effective protease catalysis approach. Various proteases were evaluated as catalysts and -chymotrypsin was found to be most efficient. Papain, which was highly active for the oligomerization of L-glutamic acid diethyl ester oligomerization was inactive for L-aspartic acid diethyl ester oligomerization. The efficiency of -chymotrypsin for the synthesis of oligo(-ethyl-aspartate) was studied under various conditions (pH, temperature, buffer concentration, solvent concentration, co-solvent and reactant/catalyst concentrations). The preferred reaction conditions were pH 8.5, 40 oC, and 5 min reaction time. Chain lengths distribution of the oligopeptide obtained was 8-25. To fully understand protease specificity for this reaction, computational modeling was performed using the Rosetta software. Simulations were run to determine the relative energies of substrate docking to papain and -chymotrypsin active sites in which the respective enzyme-acyl complexes of aspartate and glutamate had been formed. These calculations provided insights into molecular determinants of the substrate selectivity for peptide bond formation for the two proteases.

Protease-catalyzed oligomerization of L-aspartic acid diethyl ester and active site computational modeling work (part 1):

In nature, small molecules known as catechols play a key role in a broad range of biochemical processes and functions. One function of catechols is to act as the ‘sticky’ group that reacts with or binds to a broad range of materials. Glues from marine mussels (Mytilus edulis), mussel proteins exhibit interesting material properties still unmatched by human technology due to their remarkable ability to strongly adhere to virtually all surfaces. However, the problem with the direct use of mussel glues is they are expensive and not readily available. We developed a cost-effective environmentally friendly bioadhesive designed by borrowing chemical and mechanistic features of mussel adhesive proteins. Catechol units containing-oligopeptides were grafted to poly(maleic anhydride)s to mimic the mechanism by which mussel adhesive proteins function and the adhesions were measured by lap shear experiments on a tensile test instrument. Aqueous solutions of this polymer were mixed with a suitable oxidizing reagent and to cross-linked into networks and formed adhesive bonds with different substrates. It was found that the adhesion was dependent on various parameters such as type of oxidants, concentration of oxidants, concentration of cationic additives and pH etc. The maximum adhesion was obtained with aluminum substrates under slightly basic condition, with the presence of poly(lysine) additive and cured for 48h.

Bioadhesives based on poly(maleic anhydride)-g-catechol functionalized oligopeptides (part 2):