Mercury increases water permeability of a plant aquaporin through a non-cysteine related mechanism

Water transport across cellular membranes is mediated by a family of membrane proteins known as aquaporins (AQP). AQPs were first discovered based on their ability to be inhibited by mercurial compounds, an experiment which has followed the aquaporin field ever since. While mercury inhibition is most common, many AQPs are mercury insensitive. In plants, regulation of AQPs is important in order to cope with environmental changes. Plant plasma membrane aquaporins are known to be gated by phosphorylation, pH and Ca2+. We have previously solved the structure of the spinach AQP SoPIP2;1 in closed and open conformations and proposed a mechanism for how this gating can be achieved. To study the effect of mercury on SoPIP2;1 we solved the structure of the SoPIP2;1-mercury complex and characterized the water transport ability using proteoliposomes. The structure revealed mercury binding to three out of four cysteines. Contrary to what is normally seen for AQPs, mercury increased the water transport rate of SoPIP2;1, an effect which could not be attributed to any of the cysteines. This indicates that other factors might influence the effect of mercury on SoPIP2;1, one of which could be the properties of the lipid bilayer.
Source: BJ Cell - Category: Biochemistry Authors: Tags: BJ Plant Source Type: research