Structure and function of AQP2
Nephrology, Dialysis and Transplantation
Aquaporin-2 (AQP2) is the vasopressin-regulated helix 5 in addition to loop E was replaced simultanwater channel and its gene mutations are known to eously with those of AQP2, the Pf value dramatically cause the defect in urine-concentrating ability resulting increased to a level not significantly different from that in a human disease, nephrogenic diabetes insipidus. To of AQP2. This result clearly showed that the region understand AQP2 protein structure, processing in the encompassing helix 5
... ncompassing helix 5 and loop E of AQP/MIP proteins cell and regulation by cAMP/vasopressin, we have is important in creating the aqueous pore through performed site-directed mutagenesis and chimera studwhich water molecules pass  . ies in oocytes and LLCPK1 expression systems. The functional role of loop B and C was examined Although interpretations were not straightforward in in a yeast expression system, where the problem of cell some cases, much information regarding AQP2 and surface expression can be avoided . Using this other aquaporins has been obtained. This information system, we showed that MIP chimeras having AQP2 together with recent three-dimensional morphological loops B or C did not show increased Pf values. This studies will determine the structure-function relationresult suggests that these loops may not be critical ship of AQP/MIP proteins. components in determining water-transporting ability in this protein family  . This may contradict the 'hourglass model' which predicts the symmetrical importance of loops B and E.