Towards a structural and functional understanding of human aquaporin 9

Other conference contribution, 2007

Human aquaporin 9 (hAQP9) is one of the glycerol channels that are a member of the aquaporin family. AQP9 have been shown to have the broadest specificity among the aquaporins. Except for glycerol and water it facilitates the transport of urea, arsenite, polyols and other small uncharged solutes. hAQP9 is partly expressed in hepatocytes and is thought to transport glycerol into the liver. Recently an electron microscopy projection map of AQP9 (from rat) was published to 7Å resolution indicating the typical aquaporin tetrameric structure. In our lab, we have successfully over expressed human AQP9 in Pichia pastoris. This system has showed to be a suitable host to express eukaryotic membrane proteins with high yield. The goal is to attain a high resolution structure that will reveal what lies behind the differences in specificity between the aquaporins and aquaglyceroporins. AQP9 has further been solubilised with Foscholine-12 (Fos-C12) and purified on a Ni-NTA resin followed by gelfiltration. The purified protein was detected by SDS-PAGE and estimated to be 90% pure. Transport studies by AQP9 of arsenite, glycerol and other polyols are performed in Saccharomyses cervisiae to prove functionality. We have successfully detected a clear sensitivity for arsenite of rAQP9 expressed in S.cerevisiae. Currently, the transport specificity for glycerol and other polyols are tested for both human and rat AQP9.