title: Minicollagen cysteine-rich domains encode distinct modes of polymerization to form stable nematocyst capsules.
abstract: The stinging capsules of cnidarians, nematocysts, function as harpoon-like organelles with unusual biomechanical properties. The nanosecond discharge of the nematocyst requires a dense protein network of the capsule structure withstanding an internal pressure of up to 150 bar. Main components of the capsule are short collagens, so-called minicollagens, that form extended polymers by disulfide reshuffling of their cysteine-rich domains (CRDs). Although CRDs have identical cysteine patterns, they exhibit different structures and disulfide connectivity at minicollagen N and C-termini. We show that the structurally divergent CRDs have different cross-linking potentials in vitro and in vivo. While the C-CRD can participate in several simultaneous intermolecular disulfides and functions as a cystine knot after minicollagen synthesis, the N-CRD is monovalent. Our combined experimental and computational analyses reveal the cysteines in the C-CRD fold to exhibit a higher structural propensity for disulfide bonding and a faster kinetics of polymerization. During nematocyst maturation, the highly reactive C-CRD is instrumental in efficient cross-linking of minicollagens to form pressure resistant capsules. The higher ratio of C-CRD folding types evidenced in the medusozoan lineage might have fostered the evolution of novel, predatory nematocyst types in cnidarians with a free-swimming medusa stage.
authors.affiliation: University of Heidelberg, Centre for Organismal Studies, Department of Molecular Evolution and Genomics, Im Neuenheimer Feld 329, 69120 Heidelberg, Germany.
authors.forename: Anja
authors.initials: A
authors.lastname: Tursch
authors.affiliation: Heidelberg Institute for Theoretical Studies, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany.|University of Heidelberg, Interdisciplinary Center for Scientific Computing, INF 368, 69118 Heidelberg, Germany.
authors.forename: Davide
authors.initials: D
authors.lastname: Mercadante
authors.affiliation: University of Heidelberg, Centre for Organismal Studies, Department of Molecular Evolution and Genomics, Im Neuenheimer Feld 329, 69120 Heidelberg, Germany.
authors.forename: Jutta
authors.initials: J
authors.lastname: Tennigkeit
authors.affiliation: Heidelberg Institute for Theoretical Studies, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany.|University of Heidelberg, Interdisciplinary Center for Scientific Computing, INF 368, 69118 Heidelberg, Germany.
authors.forename: Frauke
authors.initials: F
authors.lastname: Gräter
authors.affiliation: University of Heidelberg, Centre for Organismal Studies, Department of Molecular Evolution and Genomics, Im Neuenheimer Feld 329, 69120 Heidelberg, Germany.
authors.forename: Suat
authors.initials: S
authors.lastname: Özbek
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000918:Antibody Specificity; D003063:Cnidaria / Q000737:chemistry; D003094:Collagen / Q000737:chemistry*; D003432:Cross-Linking Reagents / Q000737:chemistry; D003545:Cysteine / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry; D005453:Fluorescence; D049452:Green Fluorescent Proteins / Q000378:metabolism; D009024:Morphogenesis; D058894:Nematocyst / Q000378:metabolism*; D058105:Polymerization; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship
chemical_list: D003432:Cross-Linking Reagents; D004220:Disulfides; D049452:Green Fluorescent Proteins; D003094:Collagen; D003545:Cysteine