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.
Mol Plant. 2016 Jul 6;9(7):1004-17. doi: 10.1016/j.molp.2016.04.012. Epub 2016 Apr 29.
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.
水通道蛋白(AQP)是一种存在于原核和真核细胞各种亚细胞膜中的水通道蛋白。AQP 的生理功能已在许多生物体中阐明。然而,它们的生物发生仍然难以捉摸,特别是关于它们如何组装成四聚体。在这里,我们使用广泛的氨基酸取代突变分析研究了拟南芥质膜 AQP AtPIP2;1 四聚体形成涉及的氨基酸残基。突变蛋白 V41A/E44A、F51A/L52A、F87A/I91A、F92A/I93A、V95A/Y96A 和 H216A/L217A 在 AtPIP2;1 的跨膜(TM)螺旋中含有丙氨酸取代,聚合形成多个寡聚复合物,亚基数量大于四。此外,这些突变蛋白未能转运到质膜,而是积累在内质网(ER)中。基于结构的建模表明,这些残基主要参与单体内部和单体之间的 TM 螺旋之间的相互作用。这些结果表明,单体内部和单体之间的 TM 相互作用在 AtPIP2;1 复合物的四聚体形成中起着至关重要的作用。此外,AtPIP2;1 四聚体的组装对于它们从 ER 到质膜的运输以及水通透性至关重要。