Structural Characteristics, Biological Functions, and Application Prospects of Mussel Adhesive Proteins

Mussel adhesive proteins (Mussel Adhesive Protein, MAP) originate from the natural adhesion system secreted by the byssal glands of marine mussels. They are macromolecular proteins enriched in 3,4-dihydroxyphenylalanine (DOPA) moieties and exhibit a distinctive capability to achieve strong yet reversible adhesion in wet and saline environments. Since systematic investigations began in the 1980s, MAP has become a central research subject in marine biomaterials and biomimetic adhesive systems, demonstrating broad application potential in medical bioadhesives, wound-repair materials, implantable device coatings, anticorrosion coatings, and skin-barrier repair. This article reviews the discovery history, molecular structure and physicochemical properties, biological functions, and representative application scenarios of MAP, and briefly analyzes the key challenges associated with large-scale preparation and engineering translation.

I、Overview and Discovery Background of Mussel Adhesive Proteins

1.1 Mussel Byssus and Natural Bioadhesion Phenomena

(1) Biological functions of mussel byssus

Marine mussels secure themselves firmly to substrates such as rocks, reefs, or ship hulls through byssal threads to withstand tidal impacts and hydrodynamic shear. Byssal threads are formed by proteins secreted from byssal glands and subsequently cured; terminal adhesive plaques adhere tightly to diverse inorganic or organic interfaces, thereby constructing a stable “multi-point anchoring” system. This adhesion process maintains high bonding strength even under high salinity, high humidity, and dynamic conditions, representing a typical marine bioadhesion mode.

(2) Byssal gland secretion and the origin of adhesive proteins

Byssal glands can continuously secrete adhesion-related proteins rich in DOPA groups; following secretion, assembly, and curing, these proteins form byssal threads and adhesive plaques with layered architectures. In industrial and laboratory preparation, MAP (also referred to as mussel byssal/foot proteins) is typically isolated from natural tissues by processing byssal threads and related glands via homogenization, chromatographic purification, and concentration. Owing to extremely low natural abundance, it has been reported that approximately 10,000 mussels yield only about 1 mg of MAP, highlighting fundamental constraints in cost and scalability for natural-source production.

1.2 Discovery and Research Milestones of MAP

(1) Research origin and interdisciplinary attention

In the 1980s, research teams in the United States first systematically proposed and identified adhesive proteins associated with mussel byssal threads, and progressively elucidated their DOPA-rich characteristics. After 1983, research on mussel adhesion systems expanded rapidly; studies on MAP structure and function were repeatedly published in high-impact journals, attracting extensive attention from materials science, surface chemistry, and biomedical engineering.

(2) Global research and industrialization landscape

Subsequently, the United States continued application-oriented research in MAP and biomimetic adhesive materials for more than 30 years; Japan, South Korea, and other countries also established related fundamental and translational programs. In China, laboratory research on MAP has been conducted for over a decade, with progress in extraction processes, structural characterization, and applications in medical and skin-repair directions; since 2014, related products have gradually entered medical and associated market applications.

II、Molecular Structure and Physicochemical Properties of MAP

2.1 Amino Acid Composition and DOPA Features

(1) Amino acid composition

Mussel byssal adhesive proteins comprise multiple subtypes, which can differ in molecular weight and repeat-sequence features. Certain subtypes exhibit repetitive peptide motifs and are enriched in residues such as glycine, serine, aspartic acid, and lysine, thereby providing a flexible backbone, a hydrophilic interface, and charged side chains that facilitate stable interactions with aqueous environments and diverse interfaces.

(2) DOPA groups and their chemical reactivity

The most characteristic structural feature of MAP is its high content of DOPA residues. DOPA can be formed by enzymatic hydroxylation of tyrosine, and its ortho-dihydroxy (catechol) side chain exhibits pronounced chemical reactivity. Under oxidative conditions, DOPA can be converted to an o-quinone structure; o-quinones can undergo covalent addition or crosslinking reactions with amines, thiols, and other nucleophilic groups, thereby forming stable covalent networks both between protein molecules and between proteins and substrates. The dynamic balance between oxidized and non-oxidized DOPA enables MAP to combine reversible adsorption with durable curing in moist environments.

2.2 Higher-Order Structure and Interface-Adhesion-Related Properties

(1) β-sheet content and flexibility

MAP contains a certain proportion of β-sheet structures, which provide necessary conformational stability and a degree of rigidity while preserving overall chain flexibility. This enables conformational adjustment upon adsorption to complex interfaces, increasing effective contact area and the number of multi-point interaction sites.

(2) Hydration, hydrogen bonding, and multi-modal interfacial interactions

MAP is overall hydrophilic and can form a highly hydrated layer at surfaces. Through hydrogen bonding, electrostatic interactions, and coordination interactions, it establishes multiple noncovalent interactions with metal oxides, inorganic material surfaces, and organic substrates. On this basis, DOPA and its oxidation products further contribute coordination bonding and covalent bonding, enabling adhesion to maintain high shear strength and durability in wet environments such as seawater and body fluids.

2.3 Biological Functions and Materials Advantages

(1) Antioxidant capacity

Phenolic hydroxyl groups on the DOPA side chain possess free-radical-scavenging and reducing capabilities that can partially buffer oxidative stress. MAP has been reported to provide sustained antioxidant protection over extended timescales (e.g., on the order of tens of hours), which is favorable for wound repair and extracellular matrix stabilization.

(2) Antibacterial properties and biocompatibility

One proposed functional contribution of MAP in natural settings is maintaining byssal surface stability under high microbial exposure. Studies indicate that its polyphenolic structure and surface chemistry can inhibit adhesion of certain bacteria and biofilm formation, while the overall protein backbone shows good biocompatibility, supporting use in conjunction with cells, tissues, and various biomaterials.

(3) Persistent protection and barrier effects in wet environments

In aqueous or body-fluid environments, MAP can form uniform and dense nanoscale coatings or gel layers at interfaces, creating a physical barrier against external stressors (including pathogenic microorganisms, particulate contaminants, and certain inflammatory mediator transport). Antioxidant and localized anti-inflammatory actions may further prolong protective effects.

III、Preparation and Engineering Challenges of MAP

3.1 Natural Extraction Routes and Limitations

(1) Natural sources and extraction processes

At present, the primary source of MAP remains mussel byssal threads and related secretory tissues. Preparation typically includes mechanical homogenization, salting-out or organic-solvent treatment, chromatographic separation, and concentration/purification steps to obtain high-purity, DOPA-rich protein fractions.

(2) Low abundance and cost constraints

Limited by mussel body size and byssal gland secretion, the amount of MAP obtainable from a single individual is extremely small; approximately tens of thousands of mussels are required to obtain milligram-level yields. This intrinsically constrains natural extraction in terms of resource utilization, environmental pressure, and economic cost, and has driven exploration of recombinant expression and biomimetic polymer strategies.

3.2 Recombinant Expression and Biomimetic Material Strategies

(1) Recombinant MAP and functional fragments

To overcome the resource bottleneck of natural extraction, researchers have used synthetic biology and protein engineering to construct recombinant polypeptides or proteins containing DOPA precursors (e.g., tyrosine-enriched sequences) in microbial or other expression systems, combined with enzymatic systems such as tyrosine hydroxylase to achieve DOPA modification. Recombinant MAP or short peptide fragments can retain core adhesive structural units, but differences from native proteins remain in terms of DOPA content, distribution, and structural integrity.

(2) DOPA-modified biomimetic polymers

Another strategy employs synthetic polymers or natural macromolecules (e.g., gelatin, hyaluronic acid, polyethylene glycol) as backbones and introduces DOPA or catechol-like groups via chemical modification to construct biomimetic mussel-adhesive polymers and hydrogel systems. These materials can be produced at larger scale under controllable conditions, and their adhesion performance and mechanical properties can be engineered by tuning catechol density, crosslinking mechanisms, and polymer backbones.

IV、Representative Application Areas of MAP

4.1 Medical Bioadhesives and Wound-Repair Materials

(1) Soft and hard tissue adhesion and alternatives to suturing

MAP can achieve efficient adhesion even in moist, body-fluid-rich environments, enabling its use as a medical bioadhesive for delicate tissues such as cornea and conjunctiva, and as an auxiliary adhesive for hard tissues such as small bone fragments and cartilage. In such applications, materials are required to exhibit good biocompatibility, appropriate biodegradability, and sufficient mechanical strength during healing to replace or assist conventional suturing.

(2) Wound repair and protection for burns and post-operative tissues

In scenarios involving skin injury caused by extensive burns, scalds, or laser treatments, MAP can serve as a functional component of wound dressings or repair coatings. It can form a dense adherent layer on moist wounds, providing a physical barrier and reducing infection risk; additionally, antioxidant and anti-inflammatory properties may help attenuate localized inflammation, promote granulation tissue formation and re-epithelialization, and partially buffer scar formation and pruritus.

4.2 Medical Devices and Functional Coatings

(1) Biofunctionalization of implant surfaces

MAP can function as an “adhesive bridge” to immobilize bioactive molecules stably on metal or polymer implant surfaces—for example, anchoring growth factors, anticoagulant molecules, or anti-inflammatory molecules on titanium or other implant surfaces—thereby constructing device coatings with defined biological functions. In drug-eluting stents, orthopedic implants, and other long-term implantable devices, MAP and biomimetic systems provide an enabling approach for durable interfacial functionalization.

(2) Anticorrosion and antifouling coatings

After adhering to metal and microelectronic surfaces, MAP can form a dense protective layer that slows the erosion of substrates by seawater, salt spray, and corrosive media. Together with synergistic effects from other anticorrosion systems, it holds promise for long-term protection of marine engineering equipment, ship structures, and microelectronic devices. Surface-chemical modulation may also inhibit microbial adhesion and biofilm formation, providing certain antifouling effects.

4.3 Skin-Barrier Repair and Personal Care Applications

(1) Barrier formation and localized anti-inflammatory/antioxidant effects

In skin care and related applications, MAP can form a uniform microscale-to-nanoscale protective film on the stratum corneum surface. Through physical barrier and hydration-layer retention effects, it can reduce transepidermal water loss and mitigate external stimuli that disrupt the skin barrier. The antioxidant and localized anti-inflammatory effects conferred by its polyphenolic structure may help attenuate skin responses under irritation or inflammatory backgrounds, supporting barrier-impaired states.

(2) Acne scarring, hyperpigmentation, and protection against environmental particulates

In applications related to post-acne atrophic scarring and post-inflammatory hyperpigmentation, MAP may help improve skin texture and pigment distribution by promoting wound repair, suppressing persistent local inflammation, and reducing oxidative stress. The surface protective layer it forms may provide partial shielding against suspended particulate matter (e.g., PM2.5), reducing opportunities for direct contact between pollutants and skin.

V、Relevant Products

Catalog No.	Product Name	Grade and Purity
rp212901	Mussel Adhesive Proteins	Animal Free，Carrier Free，sterile-filtered，Suitable for molecular biology，His-Tag，≥90%(SDS-PAGE)，DL-DOPA: ≥3%
D465042	L-dopa, Dopamine D3 receptor agonist	Moligand™, ≥98%
D111048	L-dopa	Moligand™, ≥99%
D111049	L-dopa, Agonist of GPR143	Moligand™, analytical standard, ≥99%
C110639	Catechol	Standard for GC, ≥99.5%(GC)
P431587	Catechol	sublimed grade, ≥99.5%
C110637	Catechol	AR, ≥99%

With its distinctive DOPA-enriched structure and high-efficiency wet-environment adhesion capability, MAP provides an important template for biomimetic adhesive materials and biointerface engineering. A systematic understanding of its molecular structure, physicochemical properties, and biological functions—and, on this basis, addressing the scarcity of natural sources and the challenges of engineered production—will be a key pathway to drive its transition from laboratory research toward broader clinical and industrial applications.

Aladdin: https://www.aladdinsci.com/