Molecular determinants of ammonia and urea conductance in plant aquaporin homologs

Abstract

Aquaporins and/or aquaglyceroporins regulate the permeability of plant membranes to water and small, uncharged molecules. Using molecular simulations with a plant plasma membrane aquaporin tetramer, the residues in the channel constriction region were identified as the crucial determinants of ammonia and urea conductance. The impact of these residues was experimentally verified using AtPIP2;1 pore mutants. Several, but not all, mutants with a NIP-like selectivity filter promoted yeast growth on urea or ammonia as sole sources of nitrogen. TIP-like mutants conducted urea but not NH 3 , and a residue without direct contact to the pore lumen was critical for conduction in the mutants.

AtTIP1;3 and AtTIP5;1, the only highly expressed Arabidopsis pollen‐specific aquaporins, transport water and urea

“…Therefore, AtTIP5;1 may have transport properties that are unlike conventional aquaporins, although we showed here that AtTIP5;1 transports water and specifically urea, since no transport of glycerol or boric acid was observed. Our results agreed with a previous report that showed that when the ar/R residues of AtPIP2;1 are exchanged by the AtTIP5;1 or AtTIP1;3 residues and introduced into a mutant yeast strain unable to uptake urea, yeast cells that bear the chimeric aquaporins grew under selective conditions [29].…”

The molecular processes of urea hydrolysis in relation to ammonia emissions from agriculture

“…However, studies have found that plants possess dedicated urea transporters that either actively or passively transport urea into the plant (Dynowski et al 2008;Liu et al 2003a, b). Inside the plant cells, urease hydrolyzes urea into ammonia, and the plant then uses it as a nitrogen source.…”

Ammonia permeability of the soybean nodulin 26 channel

“…The water-selective AtPIP2;1, which transports water but not NH 3 , was used as a scaffold for site-directed mutagenesis to construct ar/R regions characteristic of various Arabidopsis NIP transporters. The results show that several NIPlike mutants of both the NIP I and NIP II ar/R subclasses show the ability to complement yeast ammonia auxotrophs but that this ability also depends upon additional residues in other regions of the pore [20]. In the present study it is shown that purified soybean nod26, the NIP family archetype which has an ar/R region characteristic of NIP I pores [22], exhibits the ability to transport NH 3 and shows an approximately fourfold stronger preference for this substrate over water.…”

“…Given the similarities in van der Waals volume for water (12.4 cm 3 /mol) and NH 3 (13.8 cm 3 /mol) and similarities in their However, comparison of the transport selectivities of various aquaporins shows that this is not the case, and that the ability to select for water or ammonia transport is a property of the amino acids present within the aromatic/arginine (ar/R) selectivity filter [19][20][21]. This region is composed of a confluence of four amino acids that form the narrowest constriction within the pore and determine the selectivity of MIP/aquaporin transporters.…”

“…This region is composed of a confluence of four amino acids that form the narrowest constriction within the pore and determine the selectivity of MIP/aquaporin transporters. Dynowski and Ludewig [20] investigated the molecular determinants of ammonia transport through plant aquaporins by using molecular dynamics simulations and by yeast complementation analyses on ammonia selective media. The water-selective AtPIP2;1, which transports water but not NH 3 , was used as a scaffold for site-directed mutagenesis to construct ar/R regions characteristic of various Arabidopsis NIP transporters.…”