Aquaporins are integral membrane proteins that facilitate the transport of water and some small solutes across cellular membranes. X-ray crystallography of aquaporins indicates that four @entity1522 constitute an aromatic/ @entity369 (ar/R) pore constriction known as the selectivity filter. On the basis of these four @entity1522 , tonoplast aquaporins called tonoplast intrinsic proteins (TIPs) are divided into three groups in @entity958 . Herein, we describe the characterization of two group I TIP1s (TgTIP1;1 and TgTIP1;2) from tulip (Tulipa gesneriana). TgTIP1;1 and TgTIP1;2 have a novel @entity6778 in loop E (LE2 position) of the ar/R filter; the residue at LE2 is a @entity4857 in all group I TIPs from model plants. The homologs showed @entity349 -sensitive water channel activity in a fast kinetics swelling assay upon heterologous expression in @entity10056 . Heterologous expression of both homologs promoted the growth of @entity10056 on @entity3104 or @entity1133 as sole sources of @entity1568 and decreased growth and survival in the presence of @entity274 . TgTIP1;1- and TgTIP1;2-mediated @entity274 conductance was demonstrated further by a fluorescence assay. Substitutions in the ar/R selectivity filter of TgTIP1;1 showed that mutants that mimicked the ar/R constriction of group I TIPs could conduct the same substrates that were transported by wild-type TgTIP1;1. In contrast, mutants that mimicked group II TIPs showed no evidence of @entity1133 or @entity274 conductance. These results suggest that the @entity535 residue at LE2 position is critical for the transport selectivity of the TIP homologs and group I TIPs might have a broader spectrum of substrate selectivity than group II TIPs.

Substitution of a single @entity535 residue in the aromatic/ XXXX selectivity filter alters the transport profiles of tonoplast aquaporin homologs.

@entity1522 :: ('CHEBI:33709', 'Chemical') :: ['amino acids'] @entity1568 :: ('MESH:D009584', 'Chemical') :: ['nitrogen'] @entity274 :: ('CHEBI:16240', 'Chemical') :: ['H(2)O(2)'] @entity1133 :: ('MESH:D014508', 'Chemical') :: ['urea'] @entity958 :: ('3702', 'Species') :: ['Arabidopsis'] @entity349 :: ('MESH:D008628', 'Chemical') :: ['mercury'] @entity10056 :: ('4922', 'Species') :: ['Pichia pastoris', 'P. pastoris'] @entity535 :: ('CHEBI:33704', 'Chemical') :: ['amino acid'] @entity6778 :: ('CHEBI:24898', 'Chemical') :: ['isoleucine'] @entity4857 :: ('CHEBI:27266', 'Chemical') :: ['valine'] @entity3104 :: ('MESH:D000644', 'Chemical') :: ['ammonium'] @entity369 :: ('CHEBI:29016', 'Chemical') :: ['arginine']
@entity369 :: (CHEBI:29016,Chemical) :: ['arginine']
