Mussel attachment on rocky shores: the effect of flow on byssus production

Mussels rely on a strong byssal attachment to persist in a range of habitats with differing rates of water flow. Recent studies, however, suggest that the ability of one mussel species to sense and respond adaptively to the flow in its environment is limited under even modest flow conditions because the process of byssal thread formation is disrupted. This study extends these findings to four mussel species, Mytilus trossulus, M. galloprovincialis, M. californianus, and Modiolus modiolus. Collectively, the response of byssal thread formation decreased with rates of flow above ～25 cm/s and the critical flow threshold was estimated to be <50 cm/s. How can mussels persist on shores where flow is an order of magnitude higher? Using a combination of techniques for measuring flow, velocity profiles were obtained above and within mussel aggregations in the laboratory and in the field. Flow was greatly reduced within mussel aggregations, ranging from 0.1% to 10% of free-stream velocity. These results suggest one key to the success of mussels in habitats with high rates of flow is the ability to form aggregations that ameliorate flows to a level that is conducive to byssal thread formation.     

Functional nanoscale biomolecular materials

Various approaches have been developed to exploit the functional properties of proteins and the structural properties of nanoscale materials. These range from biomolecule-nanomaterial hybrids and biocatalytically-generated self-assembled amphiphiles to protein-based structural templates. This commentary by Jonathan Dordick, discusses the article by Douglas Clark and colleagues, in which the authors report a study on the extremophilic protein γ-prefoldin (γPFD). See accompanying article by Dominic J. Glover et al. DOI: 10.1002/biot.201200009     

Composition and ultrastructure of the byssus of Mytilus edulis

Three regions of the byssus of the marine mussel Mytilus edulis L. are distinct in structural organization at the macroscopic and microscopic level and in amino acid composition. The threads that emanate from the stem at the base of the foot are divided into two regions. The proximal, elastic region has a crimped, densely staining cortex enclosing an interior matrix of spiral fibers, and its amino acid composition reflects protein heterogeneity. The more distal, rigid region has a straight, tubular cortex surrounding an inner matrix of linearly arranged bundles of fibrils and has a composition approximating pure collagen. The plaque, or disc-shaped portion, which mediates attachment to various substrates, is distinguished by a surface matrix of collagen-like fibers similar to those of the thread region and anchored on an inner spongy matrix. Compositional evidence exists for a collagenous component, a catechol-rich protein, and at least one other accessory protein in the plaque.     

Capillary biomolecular separations

This article summarizes the recent advances in microcolumn separations of biopolymers. Microcolumn liquid chromatography is primarily emphasized for its role as a micropreparative and fractionation tool, whereas high-performance capillary electrophoresis is demonstrated as a highly efficient technique for final analyses. Following a brief discussion of new trends in instrumentation, the recent applications of capillary techniques to proteins, DNA and glycoconjugates are reviewed.     

贻贝的黏着机制

贻贝通过足丝（byssus）分泌的贻贝黏着蛋白质（mussel adhesive protein,MAP）能附着在海水中的任何有机物和无机物表面,目前认为贻贝黏着蛋白质中含高浓度特殊的氨基酸DOPA（3,4-二羟基苯丙氨酸）在贻贝黏附过程中扮演重要的角色。DOPA能直接与金属氧化物通过有机金属络合反应形成稳定的络合物,也能在氧化后与其同一多肽链上或不同多肽链上的其他残基形成稳定的交联结构,进而牢固黏附于物体表面。贻贝黏着蛋白质具有黏合范围广、速度快、耐腐蚀、强度高和生物亲和性良好等优点,被认为是极好的广谱生物胶黏剂而应用于医学和生物工程等领域。     

Interspecific comparison of the mechanical properties of mussel byssus

Byssally tethered mussels are found in a variety of habitats, including rocky intertidal, salt marsh, subtidal, and hydrothermal vents. One key to the survival of mussels in these communities is a secure attachment, achieved by the production of byssal threads. Although many studies have detailed the unique biomechanical properties of byssal threads, only a few prevalent species have been examined. This study assesses the variation in the mechanical properties of byssus in a broad range of mussel species from diverse environments, including intertidal and subtidal Mytilus edulis, Modiolus modiolus, Geukensia demissa, Bathymodiolus thermophilus, and Dreissena polymorpha. A tensometer was used to measure quasi-static and dynamic mechanical properties of individual threads, and several aspects of morphology were quantified. The results indicate that thread mechanical properties vary among mussel species, and several novel properties were observed. For example, of the species examined, D. polymorpha threads were the strongest, stiffest, least resilient, and fastest to recover after partial deformation. Threads of M. modiolus were characterized by the presence of two distinct yield regions prior to tensile failure. This comparative study not only provides insight into the ecological limitations and evolution of mussels, but also suggests new models for the design of novel biomimetic polymers.     

The structure and formation of the byssus attachment plaque in Mytilus

The byssus attachment plaque and the tissues responsible for its formation were studied in M. califomianus by light microscopy and by transmission and scanning electron microscopy. It was shown that the plaque consists of at least three phases which ultrastructurally resemble three secretions considered to be collagen, mucoid material and polyphenol. The mucoid and polyphenol appear to mix as a colloidal suspension in which the latter is the continuous phase and forms the definitive bonding surface. Plaque collagen represents an extension of thread material into the cementing substance. Stimulated secretion within the ducts and distal depression of the mussel's foot shows a continuum of increasing heterogeneity from the inner toward the outer regions. This reflects the distribution of exocrine cell apices wherein exocytosis of polyphenol granules predominate deeply, mucous granules superficially and collagen granules in between. It is proposed that the morphology of the plaque conforms to theoretical physical-chemical requirements for adhesion under water.     

Probing the adhesive footprints of Mytilus californianus byssus

California mussels Mytilus californianus owe their tenacity to a holdfast known as the byssus, a fibrous extracellular structure that ends distally in flattened adhesive plaques. The "footprints" of freshly secreted plaques deposited onto glass coverslips were shown by matrix-assisted laser desorption ionization time of flight mass spectrometry to consist chiefly of proteins ranging in mass from 5200 to 6700 Da. These proteins, variants of a family known as mcfp3 (M. californianus foot protein 3), were purified from acetic acid/urea extracts of plaques and foot tissue. Mcfp3 appears to sort into fast and slow electrophoretic variants. Both are rich in Gly and Asn and exhibit post-translational hydroxylation of Tyr and Arg to Dopa and 4-hydroxyarginine, respectively, with the fast variant containing more than twice as much Lys + Arg. Both the slow and fast variants were partially sequenced from the N terminus, and the complete sequences of 12 variants were deduced from cDNA using degenerate oligonucleotides, PCR, and rapid amplification of cDNA ends. Mcfp3s are highly polar molecules and contain up to 28 mol % Dopa, which remains intact and may be crucial for adhesion to metal and mineral surfaces.     

Understanding Marine Mussel Adhesion

In addition to identifying the proteins that have a role in underwater adhesion by marine mussels, research efforts have focused on identifying the genes responsible for the adhesive proteins, environmental factors that may influence protein production, and strategies for producing natural adhesives similar to the native mussel adhesive proteins. The production-scale availability of recombinant mussel adhesive proteins will enable researchers to formulate adhesives that are water-impervious and ecologically safe and can bind materials ranging from glass, plastics, metals, and wood to materials, such as bone or teeth, biological organisms, and other chemicals or molecules. Unfortunately, as of yet scientists have been unable to duplicate the processes that marine mussels use to create adhesive structures. This study provides a background on adhesive proteins identified in the blue mussel, Mytilus edulis, and introduces our research interests and discusses the future for continued research related to mussel adhesion.     

Mussel micronucleus cytome assay

The micronucleus (MN) assay is one of the most widely used genotoxicity biomarkers in aquatic organisms, providing an efficient measure of chromosomal DNA damage occurring as a result of either chromosome breakage or chromosome mis-segregation during mitosis. The MN assay is today applied in laboratory and field studies using hemocytes and gill cells from bivalves, mainly from the genera Mytilus. These represent 'sentinel' organisms because of their ability to survive under polluted conditions and to accumulate both organic and inorganic pollutants. Because the mussel MN assay also includes scoring of different cell types, including necrotic and apoptotic cells and other nuclear anomalies, it is in effect an MN cytome assay. The mussel MN cytome (MUMNcyt) assay protocol we describe here reports the recommended experimental design, sample size, cell preparation, cell fixation and staining methods. The protocol also includes criteria and photomicrographs for identifying different cell types and scoring criteria for micronuclei (MNi) and nuclear buds. The complete procedure requires approximately 10 h for each experimental point/sampling station (ten animals).     

贻贝抗菌肽的研究进展

贻贝中存在多种抗菌肽,根据一级结构的不同分为4种：defensin(防卫肽)、mytilin、myticin和mytimycin。抗菌肽以前体的形式存在,在缺乏感染等刺激物的情况下。成熟前体以活性方式储存在血液中,当受到感染后便参与组织反应。它们的抗感染反应与哺乳动物吞噬细胞的作用相似,不同的抗菌肽具有不同的抗菌谱。抗菌肽是机体在进化过程中非特异性免疫系统中的一种。