Insights into structural mechanisms of gating induced regulation of aquaporins

Aquaporin family comprises of transmembrane channels that are specialized in conducting water and certain small, uncharged molecules across cell membranes. Essential roles of aquaporins in various physiological and pathophysiological conditions have attracted great scientific interest. Pioneering structural studies on aquaporins have almost solved the basic question of mechanism of selective water transport through these channels. Another important structural aspect of aquaporins which seeks attention is that how the flow of water through the channel is regulated by the mechanism of gating. Aquaporins are also regulated at the protein level, i.e. by trafficking which includes changes in their expression levels in the membrane. Availability of high resolution structures along with numerous molecular dynamics simulation studies have helped to gain an understanding of the structural mechanisms by which water flux through aquaporins is controlled. This review will summarize the highlights regarding structural features of aquaporins, mechanisms governing water permeation, proton exclusion and substrate specificity, and describe the structural insights into the mechanisms of aquaporin gating whereby water conduction is regulated by post translational modifications, such as phosphorylation.