Coral Mucus: The Properties of Its Constituent Mucins

Mucus carbohydrate composition correlates with scleractinian coral phylogeny

The mucus surface layer serves vital functions for scleractinian corals and consists mainly of carbohydrates. Its carbohydrate composition has been suggested to be influenced by environmental conditions (e.g., temperature, nutrients) and microbial pressures (e.g., microbial degradation, microbial coral symbionts), yet to what extend the coral mucus composition is determined by phylogeny remains to be tested. To investigate the variation of mucus carbohydrate compositions among coral species, we analyzed the composition of mucosal carbohydrate building blocks (i.e., monosaccharides) for five species of scleractinian corals, supplemented with previously reported data, to discern overall patterns using cluster analysis. Monosaccharide composition from a total of 23 species (belonging to 14 genera and 11 families) revealed significant differences between two phylogenetic clades that diverged early in the evolutionary history of scleractinian corals (i.e., complex and robust; p = 0.001, R2 = 0.20), mainly driven by the absence of arabinose in the robust clade. Despite considerable differences in environmental conditions and sample analysis protocols applied, coral phylogeny significantly correlated with monosaccharide composition (Mantel test: p < 0.001, R2 = 0.70). These results suggest that coral mucus carbohydrates display phylogenetic dependence and support their essential role in the functioning of corals.

Proteomic analysis of the mucus of the photosynthetic sea slug Elysia crispata

Elysia crispata is a tropical sea slug that can retain intracellular functional chloroplasts from its algae prey, a mechanism termed kleptoplasty. This sea slug, like other gastropods, secretes mucus, a viscous secretion with multiple functions, including lubrication, protection, and locomotion. This study presents the first comprehensive analysis of the mucus proteome of the sea slug E. crispata using gel electrophoresis and HPLC-MS/MS. We identified 306 proteins in the mucus secretions of this animal, despite the limited entries for E. crispata in the Uniprot database. The functional annotation of the mucus proteome using Gene Ontology identified proteins involved in different functions such as hydrolase activity (molecular function), carbohydrate-derived metabolic processes (biological processes) and cytoskeletal organization (cell component). Moreover, a high proportion of proteins with enzymatic activity in the mucus of E. crispata suggests potential biotechnological applications including antimicrobial and antitumor activities. Putative antimicrobial properties are reinforced by the high abundance of hydrolases. This study also identified proteins common in mucus samples from various species, supporting a common mechanism of mucus in protecting cells and tissues while facilitating animal movement. SIGNIFICANCE: Marine species are increasingly drawing the interest of researchers for their role in discovering new bioactive compounds. The study "Proteomic Analysis of the Mucus of the Photosynthetic Sea Slug Elysia crispata" is a pioneering effort that uncovers the complex protein content in this fascinating sea slug's mucus. This detailed proteomic study has revealed proteins with potential use in biotechnology, particularly for antimicrobial and antitumor purposes. This research is a first step in exploring the possibilities within the mucus of Elysia crispata, suggesting the potential for new drug discoveries. These findings could be crucial in developing treatments for severe diseases, especially those caused by multidrug-resistant bacteria, and may lead to significant advances in medical research.

Are Physical Sunscreens Safe for Marine Life? A Study on a Coral-Zooxanthellae Symbiotic System

Limited toxic and ecological studies were focused on physical sunscreen that is considered to have "safer performance", in which nanosize zinc oxide (nZnO) and nanosize titanium dioxide (nTiO2) generally are added as ultraviolet filters. Herein, the common button coral Zoanthus sp. was newly used to assess the toxic effects and underlying mechanisms of physical sunscreen. Results showed that physical sunscreen induced severe growth inhibition effects and largely compelled the symbiotic zooxanthellae, indicating that their symbiotic systems were threatened and, also, that neural and photosynthesis functions were influenced. Zn2+ toxicity and bioaccumulation were identified as the main toxic mechanisms, and nTiO2 particles released from physical sunscreen also displayed limited bioattachment and toxicity. Oxidative stress, determined by increased reactive oxygen species, superoxide dismutase, and malondialdehyde content, was indicated as another important toxic mechanism. Furthermore, when Zoanthus sp. was restored, the inhibited individual coral could be largely recovered after a short (3 d) exposure time; however, a longer exposure time damaged the coral irretrievably, which revealed the latent environmental risks of physical sunscreen. This study investigated the toxic effect of physical sunscreen on Zoanthus sp. in a relatively comprehensive manner, thus providing new insights into the toxic response of sunscreen on marine organisms.

Methods and Strategies to Uncover Coral-Associated Microbial Dark Matter

The vast majority of environmental microbes have not yet been cultured, and most of the knowledge on coral-associated microbes (CAMs) has been generated from amplicon sequencing and metagenomes. However, exploring cultured CAMs is key for a detailed and comprehensive characterization of the roles of these microbes in shaping coral health and, ultimately, for their biotechnological use as, for example, coral probiotics and other natural products. Here, the strategies and technologies that have been used to access cultured CAMs are presented, while advantages and disadvantages associated with each of these strategies are discussed. We highlight the existing gaps and potential improvements in culture-dependent methodologies, indicating several possible alternatives (including culturomics and in situ diffusion devices) that could be applied to retrieve the CAM "dark matter" (i.e., the currently undescribed CAMs). This study provides the most comprehensive synthesis of the methodologies used to recover the cultured coral microbiome to date and draws suggestions for the development of the next generation of CAM culturomics.

Transcriptional response of the azooxanthellate octocoral Scleronephthya gracillimum to seawater acidification and thermal stress

The stress responses to increased seawater temperature and marine acidification were investigated using a microarray to reveal transcriptional changes in S. gracillimum. For the study, corals were exposed to different stress experiments; high temperature only (26 °C, 28 °C and 30 °C), low-pH only (pH 7.5, pH 7.0 and pH 6.5) and dual stress experiments (28 °C + pH 7.8, 28 °C + pH 7.5 and 28 °C + pH 7.0), mortality and morphological changes in 24 h exposure experiments were investigated. The survival rates of each experimental group were observed. The gene expression changes in single and dual stress exposed coals were measured and the differentially expressed genes were classified with gene ontology analysis. The top three enriched gene ontology terms of DEGs in response to dual stress were metal ion binding (23.4%), extracellular region (17.2%), and calcium ion binding (12.8%). The gene showing the greatest increase in expression as a response to the dual stress was hemagglutinin/amebocyte aggregation factor, followed by interferon-inducible GTPase 5 and the gene showing the greatest decrease as a response to the dual stress was Fas-associating death domain-containing protein, followed by oxidase 2. These results represented the transcriptomic study focused on the stress responses of the temperate asymbiotic soft coral exposed to single and dual stresses. The combined effect of thermal and acidification stress on corals triggered the negative regulation of ion binding and extracellular matrix coding genes and these genes might serve as a basis for research into coral-specific adaptations to stress responses and global climate change.

Identification, diversity and domain structure analysis of mucin and mucin-like genes in sea anemone Actinia tenebrosa

Background

Mucins are part of the glycoprotein family and the main proteinaceous component of mucus. The sea anemone species, Actinia tenebrosa (Phylum Cnidaria) produce large amounts of mucus, which have not been studied in detail. Furthermore, there has only been limited investigation of mucin genes in phylum Cnidaria. Therefore, the aim of current study was to identify and analyse the repertoire mucin genes present in A. tenebrosa and range of other sea anemone species to document their diversity in this group.

Methods

To achieve this aim, we undertook transcriptome sequencing, assembly, and annotation to identify mucin genes in A. tenebrosa.

Results

The results from this study demonstrated a diverse repertoire of mucin proteins, including mucin1-like, mucin4-like, and a range of mucin-like genes in the range of sea anemone species examined. The domain structure of the identified mucin genes was found to be consistent with the conserved domains found in the homologous proteins of vertebrate species. The discovery of a diverse range of mucin genes in sea anemone species provided a basic reference for future mucin studies in cnidarians and could lead to research into their application in the pharmacological, clinical, and cosmetic industries.

Mechanisms and potential immune tradeoffs of accelerated coral growth induced by microfragmentation

Microfragmentation is the act of cutting corals into small pieces (~1 cm²) to accelerate the growth rates of corals relative to growth rates observed when maintaining larger-sized fragments. This rapid tissue and skeletal expansion technique offers great potential for supporting reef restoration, yet the biological processes and tradeoffs involved in microfragmentation-mediated accelerated growth are not well understood. Here we compared growth rates across a range of successively smaller fragment sizes in multiple genets of reef-building corals, Orbicella faveolata and Montastraea cavernosa. Our results confirm prior findings that smaller initial sizes confer accelerated growth after four months of recovery in a raceway. O. faveolata transcript levels associated with growth rate include genes encoding carbonic anhydrase and glutamic acid-rich proteins, which have been previously implicated in coral biomineralization, as well as a number of unannotated transcripts that warrant further characterization. Innate immunity enzyme activity assays and gene expression results suggest a potential tradeoff between growth rate after microfragmentation and immune investment. Microfragmentation-based restoration practices have had great success on Caribbean reefs, despite widespread mortality among wild corals due to infectious diseases. Future studies should continue to examine potential immune tradeoffs throughout the microfragmentation recovery period that may affect growout survival and disease transmission after outplanting.

Purified mucins in drug delivery research

One of the main challenges in the field of drug delivery remains the development of strategies to efficiently transport pharmaceuticals across mucus barriers, which regulate the passage and retention of molecules and particles in all luminal spaces of the body. A thorough understanding of the molecular mechanisms, which govern such selective permeability, is key for achieving efficient translocation of drugs and drug carriers. For this purpose, model systems based on purified mucins can contribute valuable information. In this review, we summarize advances that were made in the field of drug delivery research with such mucin-based model systems: First, we give an overview of mucin purification procedures and discuss the suitability of model systems reconstituted from purified mucins to mimic native mucus. Then, we summarize techniques to study mucin binding. Finally, we highlight approaches that made use of mucins as building blocks for drug delivery platforms or employ mucins as active compounds.

Effect of fine-scale habitat differences on algal colonisation in a coral-dominated subtropical reef

Maintaining the coexistence of algae and corals depends on the interactions between them. We investigated these interactions to assess: (1) recruitment patterns of algal turfs over time in dead areas on live corals; (2) the influence of fine-scale differences in coral-dominated environments on algal colonisation; (3) the influence of coral as a substrate for algal recruitment; (4) the invasion potential of algal turf on live coral tissue. This study compared algal colonisation directly on dead or damaged coral areas with algal colonisation on recruitment plates in coral-dominated or -free areas at 23, 154, and 230 days. We also monitored coral colonies over 1.5 years. Filamentous and articulated coralline algae were primarily evident in the early colonisation, reaching stability after 154 days. On a fine scale, the coral-dominated environment showed an increase in number of algal species and coverage. However, coral substrate was selective, with fewer species recruited to this substrate compared to the artificial plates. Furthermore, the competitive dynamics between corals and algal turfs did not result in a winner over time. Thus, algal turf colonisation was influenced not only by coral substrate but also by the reef environment on a fine scale.

High spatial resolution mapping of the mucosal proteome of the gills of Crassostrea virginica: implication in particle processing

In the oyster Crassostrea virginica, the organization of the gill allows bidirectional particle transport where a dorsal gill tract directs particles meant to be ingested while a ventral tract collects particles intended to be rejected as pseudofeces. Previous studies showed that the transport of particles in both tracts is mediated by mucus. Consequently, we hypothesized that the nature and/or the quantity of mucosal proteins present in each tract is likely to be different. Using endoscopy-aided micro-sampling of mucus from each tract followed by multidimensional protein identification technologies, and in situ hybridization, a high spatial resolution mapping of the oyster gill proteome was generated. Results showed the presence in gill mucus of a wide range of molecules involved in non-self recognition and interactions with microbes. Mucus composition was different between the two tracts, with mucus from the ventral tract shown to be rich in mucin-like proteins, providing an explanation of its high viscosity, while mucus from the dorsal tract was found to be enriched in mannose-binding proteins, known to be involved in food particle binding and selection. Overall, this study generated high-resolution proteomes for C. virginica gill mucus and demonstrated that the contrasting functions of the two pathways present on oyster gills are associated with significant differences in their protein makeup.

Cold-water coral (Lophelia pertusa) response to multiple stressors: High temperature affects recovery from short-term pollution exposure

There are numerous studies highlighting the impacts of direct and indirect stressors on marine organisms, and multi-stressor studies of their combined effects are an increasing focus of experimental work. Lophelia pertusa is a framework-forming cold-water coral that supports numerous ecosystem services in the deep ocean. These corals are threatened by increasing anthropogenic impacts to the deep-sea, such as global ocean change and hydrocarbon extraction. This study implemented two sets of experiments to assess the effects of future conditions (temperature: 8 °C and 12 °C, pH: 7.9 and 7.6) and hydrocarbon exposure (oil, dispersant, oil + dispersant combined) on coral health. Phenotypic response was assessed through three independent observations of diagnostic characteristics that were combined into an average health rating at four points during exposure and recovery. In both experiments, regardless of environmental condition, average health significantly declined during 24-hour exposure to dispersant alone but was not significantly altered in the other treatments. In the early recovery stage (24 hours), polyp health returned to the pre-exposure health state under ambient temperature in all treatments. However, increased temperature resulted in a delay in recovery (72 hours) from dispersant exposure. These experiments provide evidence that global ocean change can affect the resilience of corals to environmental stressors and that exposure to chemical dispersants may pose a greater threat than oil itself.

Concentration-independent mechanics and structure of hagfish slime

The defense mechanism of hagfish slime is remarkable considering that hagfish cannot control the concentration of the resulting gel directly; they simply exude a concentrated material into a comparably "infinite" sea of water to form a dilute, sticky, cohesive elastic gel. This raises questions about the robustness of gel formation and rheological properties across a range of concentrations, which we study here for the first time. Across a nearly 100-fold change in concentration, we discover that the gel has similar viscoelastic time-dependent properties with constant power-law exponent (α=0.18±0.01), constant relative damping tanδ=G^''/G^'≈0.2-0.3, and varying overall stiffness that scales linearly with the concentration (∼c^0.99±0.05). The power-law viscoelasticity (fit by a fractional Kelvin-Voigt model) is persistent at all concentrations with nearly constant fractal dimension. This is unlike other materials and suggests that the underlying material structure of slime remains self-similar irrespective of concentration. This interpretation is consistent with our microscopy studies of the fiber network. We derive a structure-rheology model to test the hypothesis that the origins of ultra-soft elasticity are based on bending of the fibers. The model predictions show an excellent agreement with the experiments. Our findings illustrate the unusual and robust properties of slime which may be vital in its physiological use and provide inspiration for the design of new engineered materials.

STATEMENT OF SIGNIFICANCE

Hagfish produce a unique gel-like material to defend themselves against predator attacks. The successful use of the defense gel is remarkable considering that hagfish cannot control the concentration of the resulting gel directly; they simply exude a small quantity of biomaterial which then expands by a factor of 10,000 (by volume) into an "infinite" sea of water. This raises questions about the robustness of gel formation and properties across a range of concentrations. This study provides the first ever understanding of the mechanics of hagfish slime over a very wide range of concentration. We discover that some viscoelastic properties of slime are remarkably constant regardless of its concentration. Such a characteristic is uncommon in most known materials.

Stress-Induced Mucus Secretion and Its Composition by a Combination of Proteomics and Metabolomics of the Jellyfish Aurelia coerulea

BACKGROUND

Jellyfish respond quickly to external stress that stimulates mucus secretion as a defense. Neither the composition of secreted mucus nor the process of secretion are well understood.

METHODS

Aurelia coerulea jellyfish were stimulated by removing them from environmental seawater. Secreted mucus and tissue samples were then collected within 60 min, and analyzed by a combination of proteomics and metabolomics using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS/MS), respectively.

RESULTS

Two phases of sample collection displayed a quick decrease in volume, followed by a gradual increase. A total of 2421 and 1208 proteins were identified in tissue homogenate and secreted mucus, respectively. Gene Ontology (GO) analysis showed that the mucus-enriched proteins are mainly located in extracellular or membrane-associated regions, while the tissue-enriched proteins are distributed throughout intracellular compartments. Tryptamine, among 16 different metabolites, increased with the largest-fold change value of 7.8 in mucus, which is consistent with its involvement in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway 'tryptophan metabolism'. We identified 11 metalloproteinases, four serpins, three superoxide dismutases and three complements, and their presence was speculated to be related to self-protective defense.

CONCLUSIONS

Our results provide a composition profile of proteins and metabolites in stress-induced mucus and tissue homogenate of A. coerulea. This provides insight for the ongoing endeavors to discover novel bioactive compounds. The large increase of tryptamine in mucus may indicate a strong stress response when jellyfish were taken out of seawater and the active self-protective components such as enzymes, serpins and complements potentially play a key role in innate immunity of jellyfish.

Evolutionary conservation of the antimicrobial function of mucus: a first defence against infection

Mucus layers often provide a unique and multi-functional hydrogel interface between the epithelial cells of organisms and their external environment. Mucus has exceptional properties including elasticity, changeable rheology and an ability to self-repair by re-annealing, and is therefore an ideal medium for trapping and immobilising pathogens and serving as a barrier to microbial infection. The ability to produce a functional surface mucosa was an important evolutionary step, which evolved first in the Cnidaria, which includes corals, and the Ctenophora. This allowed the exclusion of non-commensal microbes and the subsequent development of the mucus-lined digestive cavity seen in higher metazoans. The fundamental architecture of the constituent glycoprotein mucins is also evolutionarily conserved. Although an understanding of the biochemical interactions between bacteria and the mucus layer are important to the goal of developing new antimicrobial strategies, they remain relatively poorly understood. This review summarises the physicochemical properties and evolutionary importance of mucus, which make it so successful in the prevention of bacterial infection. In addition, the strategies developed by bacteria to counteract the mucus layer are also explored.

Zoanthid mucus as new source of useful biologically active proteins

Palythoa caribaeorum is a very common colonial zoanthid in the coastal reefs of Brazil. It is known for its massive production of mucus, which is traditionally used in folk medicine by fishermen in northeastern Brazil. This study identified biologically active compounds in P. caribaerum mucus. Crude mucus was collected during low tides by the manual scraping of colonies; samples were maintained in an ice bath, homogenized, and centrifuged at 16,000 g for 1 h at 4 °C; the supernatant (mucus) was kept at -80 °C until use. The enzymatic (proteolytic and phospholipase A₂), inhibitory (metallo, cysteine and serine proteases), and hemagglutinating (human erythrocyte) activities were determined. The results showed high levels of cysteine and metallo proteases, intermediate levels of phosholipase A₂, low levels of trypsin, and no elastase and chymotrypsin like activities. The mucus showed potent inhibitory activity on snake venom metalloproteases and cysteine proteinase papain. In addition, it showed agglutinating activity towards O⁺, B⁺, and A⁺ erythrocyte types. The hemostatic results showed that the mucus prolongs the aPTT and PT, and strongly inhibited platelet aggregation induced by arachidonic acid, collagen, epinephrine, ADP, and thrombin. The antimicrobial activity was tested on 15 strains of bacteria and fungi through the radial diffusion assay in agar, and no activity was observed. Compounds in P. caribaeorum mucus were analyzed for the first time in this study, and our results show potential pharmacological activities in these compounds, which are relevant for use in physiopathological investigations. However, the demonstration of these activities indicates caution in the use of crude mucus in folk medicine. Furthermore, the present or absent activities identified in this mucus suggest that the studied P. caribaeorum colonies were in thermal stress conditions at the time of sample collection; these conditions may precede the bleaching process in zoanthids. Hence, the use of mucus as an indicator of this process should be evaluated in the future.

Coral Food, Feeding, Nutrition, and Secretion: A Review

Tropical scleractinian corals are dependent to varying degrees on their photosymbiotic partners. Under normal levels of temperature and irradiance, they can provide most, but not all, of the host's nutritional requirements. Heterotrophy is required to adequately supply critical nutrients, especially nitrogen and phosphorus. Scleractinian corals are known as mesozooplankton predators, and most employ tentacle capture. The ability to trap nano- and picoplankton has been demonstrated by several coral species and appears to fulfill a substantial proportion of their daily metabolic requirements. The mechanism of capture likely involves mucociliary activity or extracoelenteric digestion, but the relative contribution of these avenues have not been evaluated. Many corals employ mesenterial filaments to procure food in various forms, but the functional morphology and chemical activities of these structures have been poorly documented. Corals are capable of acquiring nutrition from particulate and dissolved organic matter, although the degree of reliance on these sources generally has not been established. Corals, including tropical, deep- and cold-water species, are known as a major source of carbon and other nutrients for benthic communities through the secretion of mucus, despite wide variation in chemical composition. Mucus is cycled through the planktonic microbial loop, the benthos, and the microbial community within the sediments. The consensus indicates that the dissolved organic fraction of mucus usually exceeds the insoluble portion, and both serve as sources for the growth of nano- and picoplankton. As many corals employ mucus to trap food, a portion is taken back during feeding. The net gain or loss has not been evaluated, although production is generally thought to exceed consumption. The same is true for the net uptake and loss of dissolved organic matter by mucus secretion. Octocorals are thought not to employ mucus capture or mesenterial filaments during feeding and generally rely on tentacular filtration of weakly swimming mesozooplankton, particulates, dissolved organic matter, and picoplankton. Nonsymbiotic species in the tropics favor phytoplankton and weakly swimming zooplankton. Azooxanthellate soft corals are opportunistic feeders and shift their diet according to the season from phyto- and nanoplankton in summer to primarily particulate organic matter (POM) in winter. Cold-water species favor POM, phytodetritus, microplankton, and larger zooplankton when available. Antipatharians apparently feed on mesozooplankton but also use mucus nets, possibly for capture of POM. Feeding modes in this group are poorly known.

The properties of the mucus barrier, a unique gel--how can nanoparticles cross it?

The key criterion for a nanoparticle drug-delivery system is the ability to produce substantial bioavailability without damaging the physiological protective mechanisms. The main area for drug delivery is the aerodigestive tract. All epithelial surfaces have a membrane-bound layer and in the lung this layer is surmounted by a gel layer. In the gastrointestinal tract the membrane-bound mucin layer is covered by a mucus bilayer. The pore sizes of mucus gels are around 100 to 200 nm. Consequently, only nanoparticles in this size range could potentially penetrate without modification of these layers. To study nanoparticle permeation with results that pertain to in vivo conditions, native mucus mucin preparations must be used. Strategies to increase pores in mucus gels are discussed herein.

Coral-associated micro-organisms and their roles in promoting coral health and thwarting diseases

Over the last decade, significant advances have been made in characterization of the coral microbiota. Shifts in its composition often correlate with the appearance of signs of diseases and/or bleaching, thus suggesting a link between microbes, coral health and stability of reef ecosystems. The understanding of interactions in coral-associated microbiota is informed by the on-going characterization of other microbiomes, which suggest that metabolic pathways and functional capabilities define the 'core' microbiota more accurately than the taxonomic diversity of its members. Consistent with this hypothesis, there does not appear to be a consensus on the specificity in the interactions of corals with microbial commensals, even though recent studies report potentially beneficial functions of the coral-associated bacteria. They cycle sulphur, fix nitrogen, produce antimicrobial compounds, inhibit cell-to-cell signalling and disrupt virulence in opportunistic pathogens. While their beneficial functions have been documented, it is not certain whether or how these microbes are selected by the hosts. Therefore, understanding the role of innate immunity, signal and nutrient exchange in the establishment of coral microbiota and in controlling its functions will probably reveal ancient, evolutionarily conserved mechanisms that dictate the outcomes of host-microbial interactions, and impact the resilience of the host.

New directions in coral reef microbial ecology

Microbial processes largely control the health and resilience of coral reef ecosystems, and new technologies have led to an exciting wave of discovery regarding the mechanisms by which microbial communities support the functioning of these incredibly diverse and valuable systems. There are three questions at the forefront of discovery: What mechanisms underlie coral reef health and resilience? How do environmental and anthropogenic pressures affect ecosystem function? What is the ecology of microbial diseases of corals? The goal is to understand the functioning of coral reefs as integrated systems from microbes and molecules to regional and ocean-basin scale ecosystems to enable accurate predictions of resilience and responses to perturbations such as climate change and eutrophication. This review outlines recent discoveries regarding the microbial ecology of different microenvironments within coral ecosystems, and highlights research directions that take advantage of new technologies to build a quantitative and mechanistic understanding of how coral health is connected through microbial processes to its surrounding environment. The time is ripe for natural resource managers and microbial ecologists to work together to create an integrated understanding of coral reef functioning. In the context of long-term survival and conservation of reefs, the need for this work is immediate.

Sheep intelectin-2 co-purifies with the mucin Muc5ac from gastric mucus

Secretion of gastric mucins plays an essential role in host protection, and modifications in mucus properties are characteristic of the protective immune responses to pathogens. This study describes the purification and characterisation of sheep gastric mucins, and identification of those proteins that co-purify with mucins, with the potential to modify mucus properties. Gastric mucus was collected and pooled from four abattoir sheep and separated by CsCl density gradient centrifugation. Proteomic analysis of the mucin-containing fraction indicated the presence of gastric mucin (Muc5ac) and several co-purifying proteins, including intelectin-2 (Itln2). Further experimentation indicated that a combination of denaturation and reduction was required to fully release Itln2 from gastric mucin. A putative correlation was found between mucin-bound intelectin concentration and rheological properties in further sheep gastric mucus samples. In conclusion, this study provides the first characterisation of sheep gastric mucins and their purification partners, revealing potentially important mucin-intelectin interactions.