The invention relates to an isolated aquaporin having a bound ligand, wherein said ligand close the conformation of said aquaporin and inhibit and/or reduce water transport of said aquaporin, and/or a high resolution structure of an isolated aquaporin in a closed conformation characterized by the coordinates deposited at the Protein Data Bank ID:1Z98 and as set forth in Appendix 1, a crystal of said isolated aquaporin as well as the coordinates defining said crystal and the use of said aquaporin, and the use of the high-resolution structure as defined by the coordinates deposited at PDB ID:1Z98 and as set forth in Appendix 1, and a method to produce said aquaporin.