The arginine-facing amino acid residue of the rat aquaporin 1 constriction determines solute selectivity according to its size and lipophilicity

Abstract

Aquaporins (AQP) are transmembrane channels for small, predominantly uncharged solutes. Their selectivity is partly determined by the aromatic/arginine constriction. Ammonia is similar in size and polarity to water, yet a subset of aquaporins distinguishes between the two. We mutated the constriction of water-selective rat AQP1 to mimic that of the ammonia-permeable human AQP8 by replacing Phenylalanine 56 with histidine, Histidine 180 with isoleucine, and Cysteine 189 with glycine, alone and in combination. Only AQP1 mutants including the H180I exchange increased the ammonia and methylamine tolerance of yeast. In a second set of mutations, we replaced Histidine 180 with alanine, leucine, methionine, phenylalanine, asparagine or glutamine. AQP1 H180A was equivalent to AQP1 H180I. AQP1 H180L increased ammonia but not methylamine tolerance of yeast. AQP1 mutants with methionine, phenylalanine, asparagine or glutamine in place of Histidine 180, increased neither ammonia nor methylamine tolerance of yeast. All mutants conducted water, as judged by osmotic assays with yeast sphaeroplasts. We propose that the arginine-facing amino acid residue is the most versatile selector of aquaporin constrictions, excluding Escherichia coli glycerol facilitator-type aquaporins.

The water channel aquaporin-1a1 facilitates movement of CO2 and ammonia in zebrafish (Danio rerio) larvae

“…Water molecules pass through the hydrophilic aquapore of each monomer in single file. Selectivity is conferred by two conserved asparagine-proline-alanine (NPA) motifs located at the centre of the monomer and an aromatic/arginine (ar/R) constriction that forms the narrowest part of the channel (Tajkhorshid et al, 2002;Krenc et al, 2014). As a linear molecule with a diameter similar to that of water, CO 2 is expected to be capable of passing through the aquapores, although the ar/R constriction poses a significant barrier to CO 2 movement (Hub and de Groot, 2006;Wang et al, 2007).…”

“…The hydrophobic central pore appears to provide an energetically more favourable route for CO 2 movement (Hub and de Groot, 2006;Wang et al, 2007). Ammonia resembles water in size and polarity and should be able to move through the aquapores, but does not permeate through the ar/R constriction as efficiently as water (Krenc et al, 2014). Given that the substrate specificity of zebrafish aquaporins in general is similar to that of their tetrapod counterparts (Tingaud-Sequeira et al, 2010), it is likely that CO 2 and ammonia traverse zebrafish AQP1a1 through pathways similar to those predicted for AQP1 from other species.…”

A widened substrate selectivity filter of eukaryotic formate‐nitrite transporters enables high‐level lactate conductance

“…The location in the protein as well as the amino acid composition are reminiscent of the AQP selectivity filter, i.e., the ar/R constriction [23], where a positively charged arginine residue is situated in a hydrophobic, aromatic environment. The AQP selectivity filter restricts passage by size exclusion yielding water-specific channels (< 2.4 A diameter) [19], and AQPs with solute permeability, such as glycerol or urea (> 3.2 A) [23,[25][26][27][28][29][30].…”

Unveiling the Mechanisms of Aquaglyceroporin‐3 Water and Glycerol Permeation by Metadynamics

“…[18][19][20] Overall, all these studies have confirmed and extendedt he early sequence-based "hourglass"m odel. [22] Underneath, the pore centre is defined by two highly conserved asparagine-proline-alanine (NPA) motifs contained in the Ba nd El oops and semi-helices, whicha re responsiblef or exclusion of charged solutes. Close to the extracellular side, the aromatic/arginine selectivity filter (ar/R SF), the narrowestp oint of the pore, is responsible for size-exclusion of molecules.…”

“…Close to the extracellular side, the aromatic/arginine selectivity filter (ar/R SF), the narrowestp oint of the pore, is responsible for size-exclusion of molecules. [22] Underneath, the pore centre is defined by two highly conserved asparagine-proline-alanine (NPA) motifs contained in the Ba nd El oops and semi-helices, whicha re responsiblef or exclusion of charged solutes. [23][24][25][26][27][28] Since the first crystal structure [15] and molecular dynamics (MD) simulations [18] were obtained, water transport through AQPs has been understood to occur as as ingle-file mechanism.M Ds tudies have helpede lucidating the role of the selectivity filters and their effects on permeation of water and other small uncharged solutes.…”