Wonders of nature
Practical recombinant hybrid mussel bioadhesive
What man-made good exists that provides us both life’s necessity and luxury? A popular seafood cuisine, mussels are enjoyed all around the world. They can be smoked, boiled, or steamed to be served alone or as an ingredient of a larger dish. It can also produce beautiful pearls and jewelry. Now scientists have discovered another use for this nature’s gift.
Professor Hyung Joon Cha and his team at the Department of Chemical Engineering have developed a novel type of practical recombinant hybrid bioadhesive material that originates from marine mussels.
Mussels produce and secrete specialized adhesives that work in water allowing them to attach themselves in rough marine environments. These mussel adhesive proteins (MAPs) have been studied as a potential source of water-resistant bioadhesives for the past 25 years. They adhere tightly to substrata using the byssus, which is secreted from their foot and comprises of a bundle of threads. At the end of each thread, there is an adhesion plaque containing a water-resistant adhesive that enables the plaque to anchor to wet, solid surfaces. Strong and water-insoluble mussel adhesives have attracted interest for potential uses in biotechnological applications because they could be used as cell, tissue, or medical adhesives and have the added advantage of being environmentally friendly. This adhesion plaque is composed of five distinct types of protein ? foot proteins type 1 (fp-1) to type 5 (fp-5).
At present, Cell-Tak, a mixture of extracted MAPs and comprising mainly fp-1 and fp-2 are the only commercially available MAPs. However, the methods by which these MAPs are produced are inefficient and uneconomical: about 10,000 mussels are required to obtain one gram of Cell-Tak. As a result, high production costs can limit use, and they are only used as cell and tissue-culture adhesion agents. Therefore, recombinant DNA technology has been used and mass production of MAPs has been attempted in several expression systems. However, attempts to produce a functional MAP have failed for several reasons. Even though recombinant fp-1 decapeptide repeats have been successfully expressed as insoluble inclusion bodies in E. coli and extracted using acetic acid solution, their adhesion properties have not been fully addressed. From the mid-1990s, attempts have also been made to produce synthetic polypeptide mimics of fp-1, but these mimics have not shown biocompatibility data.
Fp-5 and fp-3, which are located at the interface between the substratum and the adhesion plaque of mussels, have been discovered during the past 10 years and they have been found to contain high levels of DOPA (L-3,4-dihydroxyphenyl alanine); indeed, the DOPA content is linearly correlated with the adhesion strength of MAPs. Previously, we have successfully shown that recombinant fp-5 with functional adhesion properties can be produced from Escherichia coli. Especially, recombinant fp-5 showed superior adhesion ability to Cell-Tak. However, soluble expression of recombinant fp-5 inhibited cell growth and led to a low production yield. Purification of fp-5 was also found to be complicated due to its adhesive property and the purification yield was very low. In addition, recombinant fp-5 was highly insoluble in aqueous buffer after purification, and thus, preparation of the highly concentrated solution required for practical use was not possible.
In this research, to overcome several of the limitations of previous MAPs, Professor Cha and his team designed and produced the novel type of hybrid MAP fp-151, which is a fusion protein comprising six fp-1 decapeptide repeats added to the N- and C-termini of fp-5 in E. coli cells. Using micro- and bulk-scale characterization and mammalian/human cell-adhesion analyses, they demonstrated that hybrid fp-151 has the potential to be a practical bioadhesive with strong adhesive ability (~10 kg subject can be attached on 1 cm2 area using 40 mg hybrid fp-151), a simple purification process (~1 g-purified protein per 1 liter-pilot-scale fed-batch bioreactor culture), proper manipulation properties (~300 g/l solubility), and high biocompatibility.
This novel hybrid mussel bioadehsive materials are now in commercialization stage as cell and tissue bioadhesive (first item) under collaboration with Kollodis Biosciences.
This research was published in Biomaterials (August) and funded by the National R&D Project for Useful Materials from Marine Organisms from the Ministry of Maritime Affairs and Fisheries, Korea.
Professor Hyung Joon Cha
Department of Chemical Engineering