title: The four-transmembrane protein IP39 of Euglena forms strands by a trimeric unit repeat.
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.
authors.affiliation: Cellular and Structural Physiology Institute, Nagoya University, Nagoya 464-8601, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Suzuki
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Ito
authors.forename: Yuji
authors.initials: Y
authors.lastname: Yamazaki
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Mineta
authors.forename: Masami
authors.initials: M
authors.lastname: Uji
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Abe
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Tani
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Fujiyoshi
authors.forename: Sachiko
authors.initials: S
authors.lastname: Tsukita
mesh_terms: D045163:Antibodies, Phospho-Specific / Q000378:metabolism; D003460:Crystallization; D018360:Crystallography, X-Ray; D005056:Euglena gracilis / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D008958:Models, Molecular; D019000:Phosphotyrosine / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization; D021122:Protein Subunits; D015800:Protozoan Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D020449:Repetitive Sequences, Amino Acid; D040681:Structural Homology, Protein
chemical_list: D045163:Antibodies, Phospho-Specific; D008565:Membrane Proteins; D021122:Protein Subunits; D015800:Protozoan Proteins; D019000:Phosphotyrosine