title: Evidence of α-helical coiled coils and β-sheets in hornet silk.
abstract: α-Helical coiled coil and β-sheet complexes are essential structural building elements of silk proteins produced by different species of the Hymenoptera. Beside X-ray scattering at wide and small angles we applied cryo-electron diffraction and microscopy to demonstrate the presence and the details of such structures in silk of the giant hornet Vespa mandarinia japonica. Our studies on the assembly of the fibrous silk proteins and their internal organization in relation to the primary chain structure suggest a 172 Å pitch supercoil consisting of four intertwined alanine-rich α-helical strands. The axial periodicity may adopt even multiples of the pitch value. Coiled coil motifs form the largest portion of the hornet silk structure and are aligned nearly parallel to the cocoon fiber axis in the same way as the membrane-like parts of the cocoon are molecularly orientated in the spinning direction. Supercoils were found to be associated with β-crystals, predominantly localized in the l-serine-rich chain sequences terminating each of the four predominant silk proteins. Such β-sheet blocks are considered resulting from transformation of random coil molecular sequences due to the action of elongational forces during the spinning process.
authors.affiliation: National Institute of Agrobiological Sciences (NIAS), Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Tsunenori
authors.initials: T
authors.lastname: Kameda
authors.affiliation: Laboratory of Electron Microscopy and Crystal Chemistry, Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nemoto
authors.affiliation: Laboratory of Electron Microscopy and Crystal Chemistry, Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ogawa
authors.affiliation: Laboratory of Polymer Controlled Synthesis, Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan.
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Tosaka
authors.affiliation: Laboratory of Electron Microscopy and Crystal Chemistry, Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kurata
authors.affiliation: Center for Materials Sciences, EM&Mlab, Philipps University of Marburg, 35032 Marburg, Germany. Electronic address: schaper@staff.uni-marburg.de.
authors.forename: Andreas K
authors.initials: AK
authors.lastname: Schaper
mesh_terms: D000818:Animals; D020285:Cryoelectron Microscopy; D019476:Insect Proteins / Q000737:chemistry* / Q000648:ultrastructure; D017433:Protein Structure, Secondary; D047011:Silk / Q000737:chemistry*; D014863:Wasps / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D019476:Insect Proteins; D047011:Silk
keywords: Cryo-electron and X-ray diffraction; Giant hornet silk; Pitch and periodicity; α-Helical coiled coils; β-Sheet structure