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J. Hoffmann, A. Gorodetskaia, and M. Hollmann (2006).
Ion pore properties of ionotropic glutamate receptors are modulated by a transplanted potassium channel selectivity filter.
Molecular and Cellular Neuroscience 33(3): 335-343.
doi: 10.1016/j.mcn.2006.08.006

The canonical potassium channel selectivity filter motif TVGYG was transplanted into ionotropic glutamate receptors (iGluRs) of the AMPA and NMDA subtype to test whether it renders the iGluRs K⁺ selective. The TVGYG motif modulated several ion pore properties of AMPA receptor as well as NMDA receptor mutants, e.g., the intra- and extracellular polyamine block, current/voltage relationships, open channel block by MK801 and Mg²⁺, and permeability for divalent cations. However, introduction of the selectivity filter failed to increase the K⁺ selectivity of homomeric AMPA and heteromeric NMDA receptor complexes, which may be due to absence of selectivity filter-stabilizing interaction sites in the iGluR pore domain. Our findings indicate that even if glutamate receptors appear to have the intrinsic capacity for K⁺ permeability, as is demonstrated by the prokaryotic, glutamate-gated, K⁺ selective GluR0, the isolated selectivity filter is not able to confer K⁺ permeability to the relatively unselective iGluR cation pore.