Graduate School of Frontier Biosciences, Osaka University


The four-transmembrane protein IP39 of Euglena forms strands by a trimeric unit repeat

Journal Nat Commun 4, 1766 (2013)
Authors Hiroshi Suzuki (1, *), Yasuyuki Ito (2, 3, *), Yuji Yamazaki (2), Katsuhiko Mineta (4), Masami Uji (2), Kazuhiro Abe (1), Kazutoshi Tani (1), Yoshinori Fujiyoshi (1) & Sachiko Tsukita (2)

  1. Cellular and Structural Physiology Institute (CeSPI), Nagoya University, Nagoya 464-8601, Japan.
  2. Laboratory of Biological Science, Graduate School of Frontier Biosciences and Graduate School of Medicine, Osaka University, Suita 565-0871, Japan.
  3. Research Fellow of the Japan Society for the Promotion of Science.
  4. Graduate School of Information Science and Technology, Hokkaido University, Kita, Sapporo, Hokkaido 060-0814, Japan.

*These authors contributed equally to this work.
Title The four-transmembrane protein IP39 of Euglena forms strands by a trimeric unit repeat
PubMed 23612307
Laboratory Biological Science Group 〈Prof. Tsukita〉
Abstract Euglenoid flagellates have striped surface structures comprising pellicles, which allow the cell shape to vary from rigid to flexible during the characteristic movement of the flagellates. In Euglena gracilis, the pellicular strip membranes are covered with paracrystalline arrays of a major integral membrane protein, IP39, a putative four-membrane-spanning protein with the conserved sequence motif of the PMP-22/EMP/MP20/Claudin superfamily. Here we report the three-dimensional structure of Euglena IP39 determined by electron crystallography. Two-dimensional crystals of IP39 appear to form a striated pattern of antiparallel double-rows in which trimeric IP39 units are longitudinally polymerised, resulting in continuously extending zigzag-shaped lines. Structural analysis revealed an asymmetric molecular arrangement in the trimer, and suggested that at least four different interactions between neighbouring protomers are involved. A combination of such multiple interactions would be important for linear strand formation of membrane proteins in a lipid bilayer.