Distinct Transport Selectivity of Two Structural Subclasses of the Nodulin-like Intrinsic Protein Family of Plant Aquaglyceroporin Channels

Citations Over TimeTop 10% of 2005 papers

Abstract

Major intrinsic proteins (MIPs) are a diverse class of integral membrane proteins that facilitate the transport of water and some small solutes across cellular membranes. X-ray structures of MIPs indicate that a tetrad of residues (the ar/R region) form a narrow pore constriction that constitutes the selectivity filter. In comparison with mammalian and microbial species, plants have a greater number and diversity of MIPs with greater than 30 genes encoding four phylogenetic subfamilies with eight different classes of ar/R sequences. The nodulin 26-like intrinsic protein (NIP) subfamily in Arabidopsis can be subdivided into two ar/R subgroups: the NIP subgroup I, which resembles the archetype of the family, soybean nodulin 26, and the NIP subgroup II, which is represented by the Arabidopsis protein AtNIP6;1. These two NIPs differ principally by the substitution of a conserved alanine (NIP subgroup II) for a conserved tryptophan (NIP subgroup I) in the helix 2 position (H2) of the ar/R filter. A comparison of the water and solute tranport properties of the two proteins was performed by expression in Xenopus laevis oocytes. Nodulin 26 is an aquaglyceroporin with a modest osmotic water permeability (P(f)) and the ability to transport uncharged solutes such as glycerol and formamide. In constrast, AtNIP6;1 showed no measurable water permeability but transported glycerol, formamide, as well as larger solutes that were impermeable to nodulin 26. By site-directed mutagenesis, we show that the H2 position is the crucial determinant that confers these transport behaviors. A comparison of the NIPs and tonoplast-intrinsic proteins (TIP) shows that the H2 residue can predict the transport profile for water and glycerol with histidine found in TIP-like aquaporins, tryptophan found in aquaglyceroporins (NIP I), and alanine found in water-impermeable glyceroporins (AtNIP6;1).

Related Papers

• → Salinity tolerance of Arabidopsis: a good model for cereals?(2007)129 cited
• Expression of a rice OsARGOS gene in Arabidopsis promotes cell division and expansion and increases organ size(2009)
• → Studies on a New Diphenylether Herbicide, HE-314(1967)1 cited
• → Studies on Binding Sites of Myeloma Proteins(1971)
• 二维Co(nip)2(py)2(H2O)2配合物的水热合成, 晶体结构和热分解机理研究(nip＝5-硝基间苯二甲酸根, py＝吡啶)(2006)