Molecular Mechanisms of How Mercury Inhibits Water Permeation through Aquaporin-1: Understanding by Molecular Dynamics Simulation

Abstract

Aquaporin (AQP) functions as a water-conducting pore. Mercury inhibits the water permeation through AQP. Although site-directed mutagenesis has shown that mercury binds to Cys189 during the inhibition process, it is not fully understood how this inhibits the water permeation through AQP1. We carried out 40 ns molecular dynamics simulations of bovine AQP1 tetramer with mercury (Hg-AQP1) or without mercury (Free AQP1). In Hg-AQP1, Cys191 (Cys189 in human AQP1) is converted to Cys-SHg+ in each monomer. During each last 10 ns, we observed water permeation events occurred 23 times in Free AQP1 and never in Hg-AQP1. Mercury binding did not influence the whole structure, but did induce a collapse in the orientation of several residues at the ar/R region. In Free AQP1, backbone oxygen atoms of Gly190, Cys191, and Gly192 lined, and were oriented to, the surface of the water pore channel. In Hg-AQP1, however, the SHg+ of Cys191-SHg+ was oriented toward the outside of the water pore. As a result, the backbone oxygen atoms of Gly190, Cys191, and Gly192 became disorganized and the ar/R region collapsed, thereby obstructing the permeation of water. We suggest that mercury disrupts the water pore of AQP1 through local conformational changes in the ar/R region.

Gene expression and localization of two types of AQP5 inXenopus tropicalisunder hydration and dehydration

“…The proteins were then transferred to an Immobilon-P membrane (Millipore, Tokyo, Japan) by electroblotting at 70 V for 1 h. The membrane was blocked in Block ace (Dainippon Sumitomo Pharma, Osaka, Japan). After a washing with TBS [0.1 M Tris·HCl (pH 8.0), 0.5 M NaCl, 0.1% polyoxyethylene (20) sorbitan monolaurate], the membrane was incubated with anti-AQP-xt5a serum diluted at 1:8,000. After a washing with TBS, the membrane was incubated with biotinylated goat anti-rabbit IgG antibody (Dako, Tokyo, Japan), and streptavidin-conjugated horseradish peroxidase (Dako).…”

“…1). Cys-182 is considered to be also the binding site for mercury, which inhibits water permeation through AQP-xt5a (20). In addition, three PKC phosphorylation sites were predicted at Ser-152, Ser-227, and Ser-232 (Fig.…”

Natural Variation of Root Hydraulics in Arabidopsis Grown in Normal and Salt-Stressed Conditions

“…Mercury, a general aquaporin blocker, acts by oxidation and binding to accessible Cys residues, thereby blocking and/or collapsing the aqueous pore (Daniels et al, 1996;Hirano et al, 2010). Propionic acid and azide both induce an intracellular acidosis, by acid loading or blocking of respiration via the cytochrome pathway respiration, respectively (Tournaire-Roux et al, 2003).…”

Identification and functional characterization of an ovarian aquaporin from the cockroachBlattella germanicaL. (Dictyoptera, Blattellidae)

“…The amino acids forming the ar/R constriction (His is replaced by the smaller amino acid Gly in aquaglyceroporins) (Beitz et al, 2006), and five other residues (P1-P5) located on the side-chains neighbouring the ar/R constriction (Froger et al, 1998), are responsible for substrate selectivity. The transport function of many AQPs is inhibited by mercurial sulfhydryl-reactive compounds, such as HgCl 2 , which block the water pore (Hirano et al, 2010;Preston et al, 1993).…”