title: CO2 transport by PIP2 aquaporins of barley.
abstract: CO2 permeability of plasma membrane intrinsic protein 2 (PIP2) aquaporins of Hordeum vulgare L. was investigated. Five PIP2 members were heterologously expressed in Xenopus laevis oocytes. CO2 permeability was determined by decrease of cytosolic pH in CO2-enriched buffer using a hydrogen ion-selective microelectrode. HvPIP2;1, HvPIP2;2, HvPIP2;3 and HvPIP2;5 facilitated CO2 transport across the oocyte cell membrane. However, HvPIP2;4 that is highly homologous to HvPIP2;3 did not. The isoleucine residue at position 254 of HvPIP2;3 was conserved in PIP2 aquaporins of barley, except HvPIP2;4, which possesses methionine instead. CO2 permeability was lost by the substitution of the Ile254 of HvPIP2;3 by methionine, while water permeability was not affected. These results suggest that PIP2 aquaporins are permeable to CO2. and the conserved isoleucine at the end of the E-loop is crucial for CO2 selectivity.
authors.affiliation: Institute of Plant Science and Resources, Okayama University, 2-20-1 Chuo, Kurashiki, 710-0046 Japan.
authors.forename: Izumi C
authors.initials: IC
authors.lastname: Mori
authors.forename: Jiye
authors.initials: J
authors.lastname: Rhee
authors.forename: Mineo
authors.initials: M
authors.lastname: Shibasaka
authors.forename: Shizuka
authors.initials: S
authors.lastname: Sasano
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kaneko
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Horie
authors.forename: Maki
authors.initials: M
authors.lastname: Katsuhara
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020346:Aquaporins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002245:Carbon Dioxide / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002463:Cell Membrane Permeability; D003600:Cytosol / Q000378:metabolism; D015870:Gene Expression; D018506:Gene Expression Regulation, Plant; D001467:Hordeum / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007532:Isoleucine; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009865:Oocytes; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D014867:Water / Q000378:metabolism; D014981:Xenopus
chemical_list: D020346:Aquaporins; D010940:Plant Proteins; D007532:Isoleucine; D014867:Water; D002245:Carbon Dioxide
keywords: Aquaporin; Barley; Carbon dioxide; Plasma membrane intrinsic protein 2