IQUIFIB   02644
INSTITUTO DE QUIMICA Y FISICOQUIMICA BIOLOGICAS "PROF. ALEJANDRO C. PALADINI"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Pore dynamics in PIP aquaporin closed state
Autor/es:
GERARDO ZERBETTO DE PALMA; ARMENTIA, LUCIANO; KARINA ALLEVA; ALIPERTI CAR, LUCIO; DARIO ESTRIN; AGUSTINA CANESSA FORTUNA; ARI ZEIDA
Lugar:
La PLata
Reunión:
Congreso; XLVII reunión de la Sociedad Argentina de Biofísica; 2018
Institución organizadora:
Sociedad Argentina de Biofísica
Resumen:
PIP are membrane proteins from the aquaporin family that facilitates water transport across plasma membrane in plants. The permeability of these channels are determined by the pore  inner structure and regulatory elements in the protein structure. Previous reports pointed to a conserved histidine residue located in loopD as a key element of the gating mechanism, trapping loopD in a closed conformation when protonated at low pH (Tournaire-Roux et al., Nature 2003, Törnroth-Horsefield et al., Nature 2006). Additionally, by means of structural data obtained from the X-ray crystallography of a PIP2, it was suggested that pore lining hydrophobic residues in loopD are also involved in the gating mechanism. These hydrophobic residues are proposed to be inserted into a cavity near the entrance of the pore when the PIP channel is in a closed conformation, modifying the inner structure of the pore.In this work we combine functional assays and classical molecular dynamics simulations of PIPs to elucidate the relationship between a pore lining hydrophobic residue in loopD (Leu 206 or Leu 197, in BvPIP2;2 or SoPIP2:1 respectively) and the pore inner structure in its vicinity.Experiments expressing wild type or L206A BvPIP2;2 in Xenopus oocytes showed that mutant PIP exhibit less transport inhibition when tested at high intracellular proton concentration. Molecular dynamics simulations of SoPIP2;1 starting from crystal structure and BvPIP2;2 homology models (both in a closed conformation) show a larger pore radius and lower water chemical potential across the pore coordinate near the mutated residue. Intrinsic permeability and hydrogen bonds between water molecules crossing the pore and pore lining residues were also analyzed from simulations. Our results suggest that, when in a closed state, Ala PIP mutants have a less hindered water transit across the pore, providing experimental evidence about the fine details of pore closure promoted after loopD conformational change.