Ligand recognition in glutamate receptors: insights from mutagenesis of the soluble a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-binding domain of glutamate receptor type D (GIuR-D) K. Keinanen**, M. Antola*, A. Kuusinen* and M. Johnsont *VTT Biotechnology and Food Research, P.O.B. 1500, FIN-02044 VTT, Espoo, Finland and tDepartment of Biochemistry and Pharmacy, Abo Akademi University and Turku Center of Biotechnology, Turku, Finland 835