title: A fast recoiling silk-like elastomer facilitates nanosecond nematocyst discharge.
abstract: 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.
authors.affiliation: Department of Molecular Evolution and Genomics, University of Heidelberg, Centre for Organismal Studies, Im Neuenheimer Feld 329, 69120, Heidelberg, Germany. Anna.beckmann@cos.uni-heidelberg.de.
authors.forename: Anna
authors.initials: A
authors.lastname: Beckmann
authors.affiliation: Heidelberg Institute for Theoretical Studies, Schloss-Wolfsbrunnenweg 35, 69118, Heidelberg, Germany. senbo.xiao@gmail.com.
authors.forename: Senbo
authors.initials: S
authors.lastname: Xiao
authors.affiliation: Applied Physics and Center for NanoScience, Ludwig Maximilian University, Amalienstr. 54, 80799, München, Germany. jochen.Mueller@physik.uni-muenchen.de.
authors.forename: Jochen P
authors.initials: JP
authors.lastname: Müller
authors.affiliation: Heidelberg Institute for Theoretical Studies, Schloss-Wolfsbrunnenweg 35, 69118, Heidelberg, Germany. davide.mercadante@h-its.org.
authors.forename: Davide
authors.initials: D
authors.lastname: Mercadante
authors.affiliation: Department of Molecular Evolution and Genomics, University of Heidelberg, Centre for Organismal Studies, Im Neuenheimer Feld 329, 69120, Heidelberg, Germany. kontakt@timm-nuechter.de.
authors.forename: Timm
authors.initials: T
authors.lastname: Nüchter
authors.affiliation: Kirchhoff Institute for Physics, Heidelberg University, Im Neuenheimer Feld 227, 69210, Heidelberg, Germany. nkroeger@kip.uni-heidelberg.de.
authors.forename: Niels
authors.initials: N
authors.lastname: Kröger
authors.affiliation: Dioptic GmbH, Bergstraße 92A, D-69469, Weinheim, Germany. langhojer@dioptic.de.
authors.forename: Florian
authors.initials: F
authors.lastname: Langhojer
authors.affiliation: Kirchhoff Institute for Physics, Heidelberg University, Im Neuenheimer Feld 227, 69210, Heidelberg, Germany. wolfgang.petrich@kip.uni-heidelberg.de.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Petrich
authors.affiliation: Department of Molecular Evolution and Genomics, University of Heidelberg, Centre for Organismal Studies, Im Neuenheimer Feld 329, 69120, Heidelberg, Germany. thomas.holstein@cos.uni-heidelberg.de.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Holstein
authors.affiliation: Applied Physics and Center for NanoScience, Ludwig Maximilian University, Amalienstr. 54, 80799, München, Germany. martin.Benoit@physik.uni-muenchen.de.
authors.forename: Martin
authors.initials: M
authors.lastname: Benoit
authors.affiliation: Heidelberg Institute for Theoretical Studies, Schloss-Wolfsbrunnenweg 35, 69118, Heidelberg, Germany. frauke.graeter@h-its.org.
authors.forename: Frauke
authors.initials: F
authors.lastname: Gräter
authors.affiliation: Department of Molecular Evolution and Genomics, University of Heidelberg, Centre for Organismal Studies, Im Neuenheimer Feld 329, 69120, Heidelberg, Germany. suat.oezbek@cos.uni-heidelberg.de.
authors.forename: Suat
authors.initials: S
authors.lastname: Özbek
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D003094:Collagen / Q000378:metabolism; D004548:Elasticity; D020724:Elastomers / Q000737:chemistry*; D005786:Gene Expression Regulation; D006829:Hydra / Q000502:physiology; D057927:Hydrophobic and Hydrophilic Interactions; D007150:Immunohistochemistry; D018625:Microscopy, Atomic Force; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D058894:Nematocyst / Q000502:physiology*; D066329:Protein Aggregates; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism / Q000648:ultrastructure; D047011:Silk / Q000737:chemistry* / Q000648:ultrastructure; D013997:Time Factors
chemical_list: D020724:Elastomers; D066329:Protein Aggregates; D011994:Recombinant Proteins; D047011:Silk; D003094:Collagen