creating what is known as a quinone bridge with lysine and binding within or
between molecules.
In the 1990s, a “protein 2” with a molecular weight of around 70,000 daltons
was found in the velum portion. Like protein 1, protein 2 also contained DOPA, but
differed in not containing either hydroxyproline or dihydroxyproline. Another
characteristic was an abundance of cysteine, which is not found in protein 1.
Japan’s Inou et al. identified protein 2 as having a structure with 11 repeating
sequences that are very similar to the cell growth factor known as epidermal growth
factor (EGF).
Structures like EGF are known to exist in proteins in the extracellular cell matrix
integrating communications between cells, but byssus protein 2 marked the first
case of it being discovered as a component in in vitro tissues such as byssi. Protein
2 is thought to create the basic structure of the velum, but the presence of sequences
shared with protein 1 at the end of the molecule raises a strong possibility that it
insolubilizes through a similar mechanism. It may also bind together with protein 1.
A third protein measuring around 6000 daltons in molecular weight has also
been discovered recently. This protein similarly contains DOPA in its amino acid
sequence, but its sequence also includes an abundance of a rare amino acid known
as hydroxyarginine (arginine with an additional hydroxyl group). Many quite
similar proteins are present in protein 2, suggesting that they form a protein family.
These proteins are also present in the velum and are thought to play an important
role in adhesion, but the details are not yet understood (Hwang 2013).
C. Creating Adhesive Proteins with Genetic Engineering
Understanding proteins’ properties and conformation will first and foremost require
refinement and purification of the proteins themselves. Purification and analysis are
rather time-consuming processes for adhesion proteins that have hardened and resist
dissolving. Recent developments in genetic analysis technology, however, have
enabled genetic cloning such that a full protein sequence can be identified quickly if
even a portion of it is known. Indeed, identification of the full sequence of protein 1
in the sea mussel is a process that takes approximate half a year; for proteins 2 and
3, genes can be isolated and the sequence determined in roughly two to three
months each. Genetic cloning has already become an essential technique for protein
research. Its advantages extend beyond the ability to efficiently determine
sequences; cloned genes can also be inserted into microorganisms and culture cells
to produce proteins.
A research group at one U.S. genetics company achieved expression from the
introduction of part of the genes from protein 1 in yeast. The resulting recombinant
protein itself could not be used to obtain adhesive proteins (as noted before, DOPA
production from tyrosine could not be generated through a hydroxyl group addition
reaction), but the researchers reported that they achieved adhesive activity by
applying catechol oxidase isolated and refined from button mushrooms and bacteria
to the recombinant protein. While it was not determined whether the protein that
they obtained had the same form as natural protein 1, the research at least
8.3 Bio Materials
243
between molecules.
In the 1990s, a “protein 2” with a molecular weight of around 70,000 daltons
was found in the velum portion. Like protein 1, protein 2 also contained DOPA, but
differed in not containing either hydroxyproline or dihydroxyproline. Another
characteristic was an abundance of cysteine, which is not found in protein 1.
Japan’s Inou et al. identified protein 2 as having a structure with 11 repeating
sequences that are very similar to the cell growth factor known as epidermal growth
factor (EGF).
Structures like EGF are known to exist in proteins in the extracellular cell matrix
integrating communications between cells, but byssus protein 2 marked the first
case of it being discovered as a component in in vitro tissues such as byssi. Protein
2 is thought to create the basic structure of the velum, but the presence of sequences
shared with protein 1 at the end of the molecule raises a strong possibility that it
insolubilizes through a similar mechanism. It may also bind together with protein 1.
A third protein measuring around 6000 daltons in molecular weight has also
been discovered recently. This protein similarly contains DOPA in its amino acid
sequence, but its sequence also includes an abundance of a rare amino acid known
as hydroxyarginine (arginine with an additional hydroxyl group). Many quite
similar proteins are present in protein 2, suggesting that they form a protein family.
These proteins are also present in the velum and are thought to play an important
role in adhesion, but the details are not yet understood (Hwang 2013).
C. Creating Adhesive Proteins with Genetic Engineering
Understanding proteins’ properties and conformation will first and foremost require
refinement and purification of the proteins themselves. Purification and analysis are
rather time-consuming processes for adhesion proteins that have hardened and resist
dissolving. Recent developments in genetic analysis technology, however, have
enabled genetic cloning such that a full protein sequence can be identified quickly if
even a portion of it is known. Indeed, identification of the full sequence of protein 1
in the sea mussel is a process that takes approximate half a year; for proteins 2 and
3, genes can be isolated and the sequence determined in roughly two to three
months each. Genetic cloning has already become an essential technique for protein
research. Its advantages extend beyond the ability to efficiently determine
sequences; cloned genes can also be inserted into microorganisms and culture cells
to produce proteins.
A research group at one U.S. genetics company achieved expression from the
introduction of part of the genes from protein 1 in yeast. The resulting recombinant
protein itself could not be used to obtain adhesive proteins (as noted before, DOPA
production from tyrosine could not be generated through a hydroxyl group addition
reaction), but the researchers reported that they achieved adhesive activity by
applying catechol oxidase isolated and refined from button mushrooms and bacteria
to the recombinant protein. While it was not determined whether the protein that
they obtained had the same form as natural protein 1, the research at least
8.3 Bio Materials
243