W0356

Structure of the Bacteriophage T4 Contracted Tail. Petr G. Leiman¹, Victor A. Kostyuchenko^1,2, Paul R. Chipman², Shuji Kanamaru², Mark van Raaij³, Fumio Arisaka⁴, Vadim V. Mesyanzhinov², and Michael G. Rossmann¹, ¹Dept. of Biological Sciences, Purdue Univ., 915 W. State St., West Lafayette, IN 47907, USA, leiman@purdue.edu, ²Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, 16/10 Miklukho-Maklaya Str, 117991 Moscow, Russia, ³Dept. de Bioquímica y Biología Molecular, Facultad de Farmacia Campus Sur, Univ. de Santiago, 15782 Santiago de Compostela, Spain, ⁴Dept. of Life Science, Faculty of Bioscience and Biotechnology, Tokyo Inst. of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8501, Japan.

The structure of the bacteriophage T4 contracted tail was determined by electron cryo-microscopy and image reconstruction technique to 17 Å resolution. The tail consists of the inner tube and the outer sheath terminated by a baseplate, to which the fibers are attached. The 1000 Å-long tail has six-fold symmetry, which was utilized in the reconstruction. The contracted sheath is composed of 144 subunits of gp18, which form a six-start right-handed helix with a pitch of 17 Å and a twist angle of 32.7º. The sheath surrounds the tail tube, which accommodates in its central channel a continuous fibrous structure, which might be the phage DNA descended from the capsid. The star-shaped baseplate is significantly flatter and wider than that in the hexagon conformation, associated with the non-contracted tail sheath. The major rearrangements in the baseplate structure occur in the proteins forming its outer rim. The short tail fibers, which are neatly “tucked” under the baseplate in the hexagon conformation, unravel so that their C-terminal domains directed towards the potential host cell surface, while their N-terminal domains remain associated with the baseplate. The baseplate conformation is probably regulated by the tilt angle of the long tail fibers with respect to the tail axis, which presumably depends on the host cell receptor binding state of the fiber.