title: Aquaporin tetramer composition modifies the function of tobacco aquaporins.
abstract: Heterologous expression in yeast cells revealed that NtAQP1, a member of the so-called PIP1 aquaporin subfamily, did not display increased water transport activity in comparison with controls. Instead, an increased CO(2)-triggered intracellular acidification was observed. NtPIP2;1, which belongs to the PIP2 subfamily of plant aquaporins, behaved as a true aquaporin but lacked a CO(2)-related function. Results from split YFP experiments, protein chromatography, and gel electrophoresis indicated that the proteins form heterotetramers when coexpressed in yeast. Tetramer composition had effects on transport activity as demonstrated by analysis of artificial heterotetramers with a defined proportion of NtAQP1 to NtPIP2;1. A single NtPIP2;1 aquaporin in a tetramer was sufficient to significantly increase the water permeability of the respective yeast cells. With regard to CO(2)-triggered intracellular acidification, a cooperative effect was observed, where maximum rates were measured when the tetramer consisted of NtAQP1 aquaporins only. The results confirm the model of an aquaporin monomer as a functional unit for water transport and suggest that, for CO(2)-related transport processes, a structure built up by the tetramer is the basis of this function.
authors.affiliation: Department of Applied Plant Sciences, Institute of Botany, Darmstadt University of Technology, D-64287 Darmstadt, Germany.
authors.forename: Beate
authors.initials: B
authors.lastname: Otto
authors.forename: Norbert
authors.initials: N
authors.lastname: Uehlein
authors.forename: Sven
authors.initials: S
authors.lastname: Sdorra
authors.forename: Matthias
authors.initials: M
authors.lastname: Fischer
authors.forename: Muhammad
authors.initials: M
authors.lastname: Ayaz
authors.forename: Xana
authors.initials: X
authors.lastname: Belastegui-Macadam
authors.forename: Marlies
authors.initials: M
authors.lastname: Heckwolf
authors.forename: Magdalena
authors.initials: M
authors.lastname: Lachnit
authors.forename: Nadine
authors.initials: N
authors.lastname: Pede
authors.forename: Nadine
authors.initials: N
authors.lastname: Priem
authors.forename: André
authors.initials: A
authors.lastname: Reinhard
authors.forename: Sven
authors.initials: S
authors.lastname: Siegfart
authors.forename: Michael
authors.initials: M
authors.lastname: Urban
authors.forename: Ralf
authors.initials: R
authors.lastname: Kaldenhoff
mesh_terms: D020346:Aquaporins / Q000235:genetics / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D012441:Saccharomyces cerevisiae; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism*; D014867:Water / Q000378:metabolism*
chemical_list: D020346:Aquaporins; D010940:Plant Proteins; D014867:Water; D002245:Carbon Dioxide