A disulfide-linked collagenous protein of nematocyst capsules

In vivo comparison of jellyfish and bovine collagen sponges as prototype medical devices

Jellyfish have emerged as a source of next generation collagen that is an attractive alternative to existing sources, such as bovine and porcine, due to a plentiful supply and providing a safer source through lack of bovine spongiform encephalopathy (BSE) transmission risk and potential viral vectors, both of which could be transmitted to humans. Here we compare collagen implantable sponges derived for the first time from the Rhizostoma pulmo jellyfish. A further novelty for the research was that there was a comparison for sponges that were either uncrosslinked or crosslinked using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), and an assessment on how this affected resorption, as well as their biocompatibility compared to bovine type I collagen sponges. The scaffolds were prepared and examined using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) and scanning electron microscopy (SEM). The samples were implanted in adult male Wistar rats for in vivo experimentation. Both crosslinked and uncrosslinked jellyfish collagen sponges showed a significant reduction in histopathology scores over the course of the study, whereas the bovine collagen sponge scores were not significantly reduced. Both jellyfish collagen sponges and the bovine sponge were tolerated well by the hosts, and a recovery was visible in all samples, suggesting that R. pulmo jellyfish-derived collagen could offer compelling biocompatibility with wound healing applications. We also demonstrate that noncrosslinked samples could be safer with better resorption times than crosslinked samples. © 2017 The Authors Journal of Biomedical Materials Research Part B: Applied Biomaterials Published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1524-1533, 2018.

The cnidome and internal morphology of Lophelia pertusa (Linnaeus, 1758) (Cnidaria, Anthozoa)

The cnidome of the scleractinian cold-water coral Lophelia pertusa (Linnaeus, 1758, syn. Lophohelia prolifera) was described by Carlgren in 1940. Due to a renewed interest in the cnidae of L. pertusa, specifically comparisons of adult and larval cnidae and their functions, we now redescribe the cnidome from material collected at the Tisler reef in Norway, close to Carlgren's collection site at Saekken (Sweden). Cnidae from column, tentacles, actinopharynx, mesenterial filaments and acontia were investigated. Fresh tissue preparations were compared to histological preparations of decalcified polyps to verify the presence of cnidocysts and secretory cells, and their composition and organization within tissues. The cnidome included microbasic b-mastigophores, microbasic and mesobasic p-mastigophores, holotrichous isorhizas and spirocysts. The nematocyst type cnidae (b-, p-mastigophores, isorhizas) appeared in different size classes with different distributions within the tissue. Spirocysts were highly variable in shape and size, without distinct size classes. In addition, developing stages of cnidae were documented, with new observations on the succession of p-mastigophore shaft development. The present observations were in general congruent with the cnidocyst descriptions from L. prolifera made by Carlgren; however, a tiny cnida, possibly of isorhiza type, has been added. Finally, the use of the term acontia is discussed.

A detailed observation of the ejection and retraction of defense tissue acontia in sea anemone (Exaiptasia pallida)

Acontia, located in the gastrovascular cavity of anemone, are thread-like tissue containing numerous stinging cells which serve as a unique defense tissue against predators of the immobile acontiarian sea anemone. Although its morphology and biological functions, such as defense and digestion, have been studied, the defense behavior and the specific events of acontia ejection and retraction are unclear. The aim of this study is to observe and record the detailed process of acontia control in anemones. Observations reveal that the anemone, Exaiptasia pallida, possibly controls a network of body muscles and manipulates water pressure in the gastrovascular cavity to eject and retract acontia. Instead of resynthesizing acontia after each ejection, the retraction and reuse of acontia enables the anemone to respond quickly at any given time, thus increasing its overall survivability. Since the Exaiptasia anemone is an emerging model for coral biology, this study provides a foundation to further investigate the biophysics, neuroscience, and defense biology of this marine model organism.

Formation of the apical flaps in nematocysts of sea anemones (cnidaria: actiniaria)

Using scanning and transmission electron microscopy, we studied formation of the structure at the apical end of sea anemone nematocysts through which the tubule everts at discharge. In anemones of the genus Metridium, we found that each of the three solid triangular apical flaps comprises two layers that are continuous with those of the capsule wall: the electron-lucent inner layer is bound to the electron-dense outer layer. The two-layer structure is obvious in some discharged capsules in which, perhaps due to fixation, the layers part at the flap's periphery. Before the nematocyst discharges, a channel leads from a pore at the tip of the joined flaps into the lumen of the inverted tubule. The thin laminate layer that coats each flap lines the channel. The base of the nematocyst tubule adheres to the capsule wall near the capsule's apical end, and a branch of the tubule underlies part of the laminate layer that coats the flaps. Thus the tubule is not continuous with the capsule wall but structurally separate from it. This helps reconcile differences in understanding of the number of layers constituting the capsule wall, and makes clear that the tubule should be considered part of the capsule contents.

Cnidarian internal stinging mechanism

Stinging mechanisms generally deliver venomous compounds to external targets. However, nematocysts, the microscopic stinging organelles that are common to all members of the phylum Cnidaria, occur and act in both external and internal tissue structures. This is the first report of such an internal piercing mechanism. This mechanism identifies prey items within the body cavity of the sea anemone and actively injects them with cytolytic venom compounds. Internal tissues isolated from sea anemones caused the degradation of live Artemia salina nauplii in vitro. When examined, the nauplii were found to be pierced by discharged nematocysts. This phenomenon is suggested to aid digestive phagocytic processes in a predator otherwise lacking the means to masticate its prey.

Sequence-structure and structure-function analysis in cysteine-rich domains forming the ultrastable nematocyst wall

The nematocyst wall of cnidarians is a unique biomaterial that withstands extreme osmotic pressures, allowing an ultrafast discharge of the nematocyst capsules. Assembly of the highly robust nematocyst wall is achieved by covalent linkage of cysteine-rich domains (CRDs) from two main protein components, minicollagens and nematocyst outer wall antigen (NOWA). The bipolar minicollagens have different disulfide patterns and topologies in their N and C-terminal CRDs. The functional significance of this polarity has been elusive. Here, we show by NMR structural analysis that all representative cysteine-rich domains of NOWA are structurally related to N-terminal minicollagen domains. Natural sequence insertions in NOWA CRDs have very little effect on the tightly knit domain structures, nor do they preclude the efficient folding to a single native conformation. The different folds in NOWA CRDs and the atypical C-terminal minicollagen domain on the other hand can be directly related to different conformational preferences in the reduced states. Ultrastructural analysis in conjunction with aggregation studies argues for an association between the similar NOWA and N-terminal minicollagen domains in early stages of the nematocyst wall assembly, which is followed by the controlled association between the unusual structures of C-terminal minicollagen domains.

The Glycoprotein NOWA and Minicollagens Are Part of a Disulfidelinked Polymer That Forms the Cnidarian Nematocyst Wall

The nematocyst is a unique extrusive organelle involved in the defense and capture of prey in cnidarians. Minicollagens and the glycoprotein NOWA are major components of the nematocyst capsule wall, which resists osmotic pressure of 15 MPa. Here we present the recombinant expression of NOWA, which spontaneously assembles to globular macromolecular particles that are sensitive to reduction as the native wall structure. Ultra-structural analysis showed that the Hydra nematocyst wall is composed of several layers of globular particles, which are interconnected via radiating rodlike protrusions. Evidence is presented that native wall particles contain NOWA and minicollagen, supposed to be linked via disulfide bonds between their homologous cysteine-rich domains. Our data suggest a continuous suprastructure of the nematocyst wall, assembled from wall proteins that share a common oligomerization motif.

Determination of a high-precision NMR structure of the minicollagen cysteine rich domain from Hydra and characterization of its disulfide bond formation

A high-precision solution structure of the C-terminal minicollagen cysteine rich domain of Hydra has been determined using modern heteronuclear and weak alignment NMR techniques at natural isotope abundance. The domain consists of only 24 amino acids, six of which are prolines and six are cysteines bonded in disulfide bridges that constrain the structure into a new fold. The redox equilibrium of the structure has been characterized from a titration with glutathione. No local native structures are detectable in the reduced form. Thus, oxidation and folding are tightly coupled.

The Structure of the Cys-rich Terminal Domain of Hydra Minicollagen, Which Is Involved in Disulfide Networks of the Nematocyst Wall

The minicollagens found in the nematocysts of Hydra constitute a family of invertebrate collagens with unusual properties. They share a common modular architecture with a central collagen sequence ranging from 14 to 16 Gly-X-Y repeats flanked by polyproline/hydroxyproline stretches and short terminal domains that show a conserved cysteine pattern (CXXXCXXXCXXX-CXXXCC). The minicollagen cysteine-rich domains are believed to function in a switch of the disulfide connectivity from intra- to intermolecular bonds during maturation of the capsule wall. The solution structure of the C-terminal fragment including a minicollagen cysteine-rich domain of minicollagen-1 was determined in two independent groups by 1H NMR. The corresponding peptide comprising the last 24 residues of the molecule was produced synthetically and refolded by oxidation under low protein concentrations. Both presented structures are identical in their fold and disulfide connections (Cys2-Cys18, Cys6-Cys14, and Cys10-Cys19) revealing a robust structural motif that is supposed to serve as the polymerization module of the nematocyst capsule.

Structure/function relationships in the minicollagen of Hydra nematocysts

The minicollagens found in the inner layer of the Hydra nematocyst walls are the smallest collagens known with 12-16 Gly-X-Y repeats. Minicollagen-1, the best characterized member of this protein family so far, consists of a central collagen triple helix of 12 nm in length flanked at both ends by a polyproline stretch and a conserved cysteine-rich domain. The cysteine-rich tails are proposed to function in the assembly of soluble minicollagen trimers to high molecular structures by a switch of the disulfide linkage from intramolecular to intermolecular bonds. In this study, we investigate the trimeric nature of minicollagen-1 and its capacity to form disulfide-linked polymers in vitro. A fusion protein of minicollagen-1 with maltose-binding protein is secreted as a soluble trimer with only intrachain and no interchain disulfide bridges as confirmed by melting the collagen triple helix under reducing and non-reducing conditions. The conversion of minicollagen-1 trimers to monomers takes place between 40 and 55 degrees C with the melting point being approximately 45 degrees C. Oxidative reshuffling of the minicollagen-1 trimers leads to the formation of high molecular aggregates, which upon reduction show distinct polytrimeric states. Minicollagen trimers in isolated nematocyst capsules proved to be sensitive to SDS and were engaged in polymeric structures with additional cross-links that were resistant to reducing agent.

A switch in disulfide linkage during minicollagen assembly in Hydra nematocysts

The smallest known collagens with only 14 Gly-X-Y repeats referred to as minicollagens are the main constituents of the capsule wall of nematocysts. These are explosive organelles found in Hydra, jellyfish, corals and other Cnidaria. Minicollagen-1 of Hydra recombinantly expressed in mammalian 293 cells contains disulfide bonds within its N- and C-terminal Cys-rich domains but no interchain cross-links. It is soluble and self-associates through non-covalent interactions to form 25-nm-long trimeric helical rod-like molecules. We have used a polyclonal antibody prepared against the recombinant protein to follow the maturation of minicollagens from soluble precursors present in the endoplasmic reticulum and post-Golgi vacuoles to the disulfide-linked insoluble assembly form of the wall. The switch from intra- to intermolecular disulfide bonds is associated with 'hardening' of the capsule wall and provides an explanation for its high tensile strength and elasticity. The process is comparable to disulfide reshuffling between the NC1 domains of collagen IV in mammalian basement membranes.

Enzymatic characterization of the major phospholipase A2 component of sea anemone (Aiptasia pallida) nematocyst venom

The purified beta phospholipase A2 (PLA2; EC 3.1.1.4) (PLA2) from sea anemone (Aiptasia pallida) nematocysts is larger and more labile than other known venom PLA2s. In common with all other known venoms and most secretory PLA2s, the beta PLA2 requires mM Ca2+ for optimal activity and is surface-activated by aggregated lipids such as mixed micelles of detergent and phospholipid. The beta PLA2 exhibits an unusually steep and narrow pH optimum of activity at pH 7.7. The effects of changes in pH on the activity of the enzyme suggest that the active site contains functional groups having a pKs of about 7.0 and 8.0. The effects of temperature on beta PLA2 activity show a marked decrease in the energy of activation above the pre-transition temperature, suggesting that the enzyme "melts" both fatty chains in order for catalysis to occur.

Spinalin, a new glycine- and histidine-rich protein in spines of Hydra nematocysts

Here we present the cloning, expression and immunocytochemical localization of a novel 24 kDa protein, designated spinalin, which is present in the spines and operculum of Hydra nematocysts. Spinalin cDNA clones were identified by in situ hybridization to differentiating nematocytes. Sequencing of a full-length clone revealed the presence of an N-terminal signal peptide, suggesting that the mature protein is sorted via the endoplasmic reticulum to the post-Golgi vacuole in which the nematocyst is formed. The N-terminal region of spinalin (154 residues) is very rich in glycines (48 residues) and histidines (33 residues). A central region of 35 residues contains 19 glycines, occurring mainly as pairs. For both regions a polyglycine-like structure is likely and this may be stabilized by hydrogen bond-mediated chain association. Similar sequences found in loricrins, cytokeratins and avian keratins are postulated to participate in formation of supramolecular structures. Spinalin is terminated by a basic region (6 lysines out of 15 residues) and an acidic region (9 glutamates and 9 aspartates out of 32 residues). Western blot analysis with a polyclonal antibody generated against a recombinant 19 kDa fragment of spinalin showed that spinalin is localized in nematocysts. Following dissociation of the nematocyst's capsule wall with DTT, spinalin was found in the insoluble fraction containing spines and the operculum. Immunocytochemical analysis of developing nematocysts revealed that spinalin first appears in the matrix but then is transferred through the capsule wall at the end of morphogenesis to form spines on the external surface of the inverted tubule and the operculum.

Novel tools for the study of development, migration and turnover of nematocytes (cnidarian stinging cells)

The rhodamine derivatives tetramethyl-rhodamine-5/6-maleimide (TROMI) and tetramethyl-rhodamine-6-isothiocyanate (TRITC) were allowed to react with living Hydra vulgaris. The two fluorescent dyes stain the polyps to different degrees, apparently without impairing their viability and behaviour. Concerning nematocytes, TROMI preferentially couples to cytoskeletal elements only of mounted nematocytes whereas TRITC selectively reacts with structural components of cysts of late nematoblasts, which thereafter develop apparently normally into mature nematocytes. Hence TROMI-labelling indicates that nematocytes are mounted and ready for discharge; TRITC-labelling can be used as a tool to investigate the final maturation, migration and installation of nematocytes in Hydra. Together with a new non-fixative method to dissociate Hydra polyps into single, identifiable cells, the two labelling methods allow direct quantitative dynamic studies of nematocyte turnover and open new possibilities of investigating the regulation and the mechanisms of nematocyte supply and migration.

Mini-collagens in hydra nematocytes

We have isolated and characterized four collagen-related c-DNA clones (N-COL 1, N-COL 2, N-COL 3, N-COL 4) that are highly expressed in developing nematocytes in hydra. All four c-DNAs as well as their corresponding transcripts are small in size (600-1,000 bp). The deduced amino acid sequences show that they contain a central region consisting of 14 to 16 Gly-X-Y triplets. This region is flanked amino-terminal by a stretch of 14-23 proline residues and carboxy-terminal by a stretch of 6-9 prolines. At the NH2- and COOH-termini are repeated patterns of cysteine residues that are highly conserved between the molecules. A model is proposed which consists of a central stable collagen triple helix of 12-14 nm length from which three 9-22 nm long polyproline II type helices emerge at both ends. Disulfide linkage between cysteine-rich segments in these helices could lead to the formation of oligomeric network structures. Electrophoretic characterization of nematocyst extracts allows resolution of small proline-rich polypeptides that correspond in size to the cloned sequences.

Characterization of nematocyst proteins from the sea anemones Aiptasia pallida and Pachycerianthus torreyi (Cnidaria: Anthozoa)

Nematocysts from the anemones Aiptasia pallida and Pachycerianthus torreyi were investigated. SDS-polyacrylamide electrophoresis of solubilized Aiptasia nematocysts revealed one major protein band (mol. wt 31,800) and several minor components. Coelectrophoresed whole venom contained numerous protein components, of which a major one appeared to be identical to the major nematocyst protein. Nematocyst capsules and everted threads from both species contained levels of glycine and proline-hydroxyproline characteristic of vertebrate collagens. Cysteine was present in significant amounts. Aiptasia whole venom contained high levels of glutamic acid and/or glutamine (71%) with no detectable cysteine or proline-hydroxyproline. The 31,800-dalton venom protein possessed only glycine (80%) and glutamyl and/or glutaminyl (20%) residues.

Invertebrate collagens

The collagens of all major invertebrate phyla have been studied, but characterization has been thorough in only a few classes and in no case in the detail (such as sequence analysis) known for vertebrate collagen. Biochemical data on insect collagen are particularly sparse. Invertebrate and vertebrate collagens are strikingly similar, with some notably unique features in annelids and nematodes. Present data do not support the suggestion that invertebrate collagens resemble vertebrate basement membrane collagen. In invertebrates, as in vertebrates, collagens of specific tissues show differenes that probably reflect individual tissue requirements.