title: Interactions between Transmembrane Helices within Monomers of the Aquaporin AtPIP2;1 Play a Crucial Role in Tetramer Formation.
abstract: Aquaporin (AQP) is a water channel protein found in various subcellular membranes of both prokaryotic and eukaryotic cells. The physiological functions of AQPs have been elucidated in many organisms. However, understanding their biogenesis remains elusive, particularly regarding how they assemble into tetramers. Here, we investigated the amino acid residues involved in the tetramer formation of the Arabidopsis plasma membrane AQP AtPIP2;1 using extensive amino acid substitution mutagenesis. The mutant proteins V41A/E44A, F51A/L52A, F87A/I91A, F92A/I93A, V95A/Y96A, and H216A/L217A, harboring alanine substitutions in the transmembrane (TM) helices of AtPIP2;1 polymerized into multiple oligomeric complexes with a variable number of subunits greater than four. Moreover, these mutant proteins failed to traffic to the plasma membrane, instead of accumulating in the endoplasmic reticulum (ER). Structure-based modeling revealed that these residues are largely involved in interactions between TM helices within monomers. These results suggest that inter-TM interactions occurring both within and between monomers play crucial roles in tetramer formation in the AtPIP2;1 complex. Moreover, the assembly of AtPIP2;1 tetramers is critical for their trafficking from the ER to the plasma membrane, as well as water permeability.
authors.affiliation: School of Interdisciplinary Bioscience and Bioengineering, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Yun-Joo
authors.initials: YJ
authors.lastname: Yoo
authors.affiliation: Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Hyun Kyung
authors.initials: HK
authors.lastname: Lee
authors.affiliation: Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Wonhee
authors.initials: W
authors.lastname: Han
authors.affiliation: Department of Biology, Sunchon National University, Sunchon 57922, Korea.
authors.forename: Dae Heon
authors.initials: DH
authors.lastname: Kim
authors.affiliation: Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Myoung Hui
authors.initials: MH
authors.lastname: Lee
authors.affiliation: Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Jouhyun
authors.initials: J
authors.lastname: Jeon
authors.affiliation: Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Dong Wook
authors.initials: DW
authors.lastname: Lee
authors.affiliation: Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Junho
authors.initials: J
authors.lastname: Lee
authors.affiliation: Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Yongjik
authors.initials: Y
authors.lastname: Lee
authors.affiliation: Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Juhun
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Jin Seok
authors.initials: JS
authors.lastname: Kim
authors.affiliation: Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Yunje
authors.initials: Y
authors.lastname: Cho
authors.affiliation: Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Jin-Kwan
authors.initials: JK
authors.lastname: Han
authors.affiliation: School of Interdisciplinary Bioscience and Bioengineering, Pohang University of Science and Technology, Pohang 790-784, Korea; Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea; Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea. Electronic address: ihhwang@postech.ac.kr.
authors.forename: Inhwan
authors.initials: I
authors.lastname: Hwang
mesh_terms: D020346:Aquaporins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D055503:Protein Multimerization / Q000235:genetics / Q000502:physiology; D017433:Protein Structure, Secondary
chemical_list: D020346:Aquaporins; D029681:Arabidopsis Proteins; C491680:plasma membrane intrinsic protein 2 Arabidopsis
keywords: AtPIP2; aquaporin; interaction between transmembrane helices; tetramer formation