title: The crystal structure of the plant small GTPase OsRac1 reveals its mode of binding to NADPH oxidase.
abstract: Rac/Rop proteins are Rho-type small GTPases that act as molecular switches in plants. Recent studies have identified these proteins as key components in many major plant signaling pathways, such as innate immunity, pollen tube growth, and root hair formation. In rice, the Rac/Rop protein OsRac1 plays an important role in regulating the production of reactive oxygen species (ROS) by the NADPH oxidase OsRbohB during innate immunity. However, the molecular mechanism by which OsRac1 regulates OsRbohB remains unknown. Here, we report the crystal structure of OsRac1 complexed with the non-hydrolyzable GTP analog guanosine 5'-(β,γ-imido)triphosphate at 1.9 Å resolution; this represents the first active-form structure of a plant small GTPase. To elucidate the ROS production in rice cells, structural information was used to design OsRac1 mutants that displayed reduced binding to OsRbohB. Only mutations in the OsRac1 Switch I region showed attenuated interactions with OsRbohB in vitro. In particular, Tyr(39) and Asp(45) substitutions suppressed ROS production in rice cells, indicating that these residues are critical for interaction with and activation of OsRbohB. Structural comparison of active-form OsRac1 with AtRop9 in its GDP-bound inactive form showed a large conformational difference in the vicinity of these residues. Our results provide new insights into the molecular mechanism of the immune response through OsRac1 and the various cellular responses associated with plant Rac/Rop proteins.
authors.affiliation: From the Institute for Protein Research, Osaka University, Suita, Osaka 565-0871.
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Kosami
authors.affiliation: the Laboratory of Biophysics and Laboratory of Plant Molecular Genetics, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, the Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, and ohki.izuru.4a@kyoto-u.ac.jp.
authors.forename: Izuru
authors.initials: I
authors.lastname: Ohki
authors.affiliation: Laboratory of Plant Molecular Genetics, Nara Institute of Science and Technology, Ikoma, Nara 630-0192.
authors.forename: Minoru
authors.initials: M
authors.lastname: Nagano
authors.affiliation: From the Institute for Protein Research, Osaka University, Suita, Osaka 565-0871.
authors.forename: Kyoko
authors.initials: K
authors.lastname: Furuita
authors.affiliation: From the Institute for Protein Research, Osaka University, Suita, Osaka 565-0871.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Sugiki
authors.affiliation: Laboratory of Plant Molecular Genetics, Nara Institute of Science and Technology, Ikoma, Nara 630-0192.
authors.forename: Yoji
authors.initials: Y
authors.lastname: Kawano
authors.affiliation: Laboratory of Plant Molecular Genetics, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, the Department of Advanced Bioscience, Kinki University, Nara 631-8505, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Kawasaki
authors.affiliation: From the Institute for Protein Research, Osaka University, Suita, Osaka 565-0871.
authors.forename: Toshimichi
authors.initials: T
authors.lastname: Fujiwara
authors.affiliation: From the Institute for Protein Research, Osaka University, Suita, Osaka 565-0871.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Nakagawa
authors.affiliation: Laboratory of Plant Molecular Genetics, Nara Institute of Science and Technology, Ikoma, Nara 630-0192.
authors.forename: Ko
authors.initials: K
authors.lastname: Shimamoto
authors.affiliation: From the Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, the Laboratory of Biophysics and kojima@protein.osaka-u.ac.jp.
authors.forename: Chojiro
authors.initials: C
authors.lastname: Kojima
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D006165:Guanylyl Imidodiphosphate / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D019255:NADPH Oxidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012275:Oryza / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics / Q000276:immunology; D010084:Oxidation-Reduction; D018129:Phosphatidylinositol Phosphates / Q000737:chemistry* / Q000378:metabolism; D057865:Plant Immunity; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017382:Reactive Oxygen Species / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D020830:rac1 GTP-Binding Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D018129:Phosphatidylinositol Phosphates; D010940:Plant Proteins; D017382:Reactive Oxygen Species; D011994:Recombinant Proteins; C055525:phosphatidylinositol 3-phosphate; D006165:Guanylyl Imidodiphosphate; D019255:NADPH Oxidases; D020559:Monomeric GTP-Binding Proteins; C512796:ROP9 protein, Arabidopsis; D020830:rac1 GTP-Binding Protein
keywords: Crystal Structure; NADPH Oxidase; Plant Defense; Rac (Rac GTPase); Rice Immunity; Small GTPase