RESUMO
BACKGROUND: The discharge of the Cnidarian stinging organelle, the nematocyst, is one of the fastest processes in biology and involves volume changes of the highly pressurised (150 bar) capsule of up to 50%. Hitherto, the molecular basis for the unusual biomechanical properties of nematocysts has been elusive, as their structure was mainly defined as a stress-resistant collagenous matrix. RESULTS: Here, we characterise Cnidoin, a novel elastic protein identified as a structural component of Hydra nematocysts. Cnidoin is expressed in nematocytes of all types and immunostainings revealed incorporation into capsule walls and tubules concomitant with minicollagens. Similar to spider silk proteins, to which it is related at sequence level, Cnidoin possesses high elasticity and fast coiling propensity as predicted by molecular dynamics simulations and quantified by force spectroscopy. Recombinant Cnidoin showed a high tendency for spontaneous aggregation to bundles of fibrillar structures. CONCLUSIONS: Cnidoin represents the molecular factor involved in kinetic energy storage and release during the ultra-fast nematocyst discharge. Furthermore, it implies an early evolutionary origin of protein elastomers in basal metazoans.
Assuntos
Elastômeros/química , Nematocisto/fisiologia , Seda/química , Sequência de Aminoácidos , Animais , Western Blotting , Colágeno/metabolismo , Elasticidade , Regulação da Expressão Gênica , Hydra/fisiologia , Interações Hidrofóbicas e Hidrofílicas , Imuno-Histoquímica , Microscopia de Força Atômica , Simulação de Dinâmica Molecular , Dados de Sequência Molecular , Agregados Proteicos , Estrutura Terciária de Proteína , Proteínas Recombinantes/metabolismo , Proteínas Recombinantes/ultraestrutura , Seda/ultraestrutura , Fatores de TempoRESUMO
Cnidarians (corals, hydras, jellyfish, sea anemones) are prey-devouring creatures with a simple nervous system, the function of which is largely unknown. A new study on the freshwater polyp Hydra has now uncovered the neuronal circuits that control its feeding behavior.
Assuntos
Antozoários , Hydra , Cifozoários , Anêmonas-do-Mar , Animais , Anêmonas-do-Mar/fisiologia , BocaRESUMO
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.