Intrinsic Motions in the N-Terminal Domain of an Ionotropic Glutamate Receptor Detected by Fluorescence Correlation Spectroscopy

Comparative Dynamics of NMDA- and AMPA-Glutamate Receptor N-Terminal Domains

“…Root-mean-square fluctuations (rmsfs) in residue positions (Figure S4) confirm that GluA3 exhibits the highest mobility among all AMPAR NTDs. This enhanced mobility is primarily mediated by LL helices αE and αF, in agreement with data from fluorescence correlation spectroscopy experiments (Jensen et al., 2011). These helices may make contacts with the LBD in the intact structure of AMPAR (Figure 1A) and could thus communicate to downstream segments of the receptor.…”

“…Utilizing a combination of X-ray structural approaches and normal mode analysis (NMA) with elastic network models (ENMs), we showed recently that the NTDs of AMPARs do have access to well-defined collective fluctuations (Sukumaran et al., 2011). Together with biophysical measurements of NTD intrinsic fluctuations (Jensen et al., 2011), these recent results exemplify the dynamic capability of non-NMDAR NTDs and suggest a potential allosteric signaling capacity, which would provide a currently unexplored target for channel modulators.…”

The N-terminal Domain Modulates α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) Receptor Desensitization

“…In fact, crystal structures of the Zn 2ϩ -bound and free NTD of the GluN2B subunit indicate that the NTD also favors a closed conformation in the absence of Zn differs from that in NMDA receptors, and a significant closure of the putative ligand-binding cleft in the AMPA receptor NTD is thought to be unlikely. AMPA receptor NTDs have, however, been shown to display flexibility (a prerequisite for an allosteric role), ranging from large-scale domain movements to more subtle conformational fluctuations (6,8,(53)(54)(55). A wide range of NTD conformations, some differing substantially from the arrangement in GluA2 cryst, have been reported on the basis of electron microscopic (16, 53, 56 -58) and atomic force microscopic (55) analyses of purified AMPA and kainate receptor preparations, supporting the view that the NTD can assume different conformations, at least under the specific experimental conditions used.…”

Functional Insights from Glutamate Receptor Ion Channel Structures

“…In the GluK5 ATD structure a glycosylation site at the entrance to the inter lobe cleft generates a steric wedge preventing further closure (61), but no such feature is present in the other ATD structures. Limited variations in the extent of ATD domain closure across iGluR subtypes, and in different crystal forms for GluA2, GluA3 and GluK2, as well as the results of normal mode analysis and fluorescence correlation spectroscopy (59, 64), suggest only small fluctuations around this partially closed conformation in AMPA and kainate receptors compared to the robust conformation changes observed in structurally related periplasmic proteins (59, 60, 64). Whether these small amplitude changes are functionally significant, and whether non NMDA receptor ATDs can undergo larger conformational changes is an important unresolved issue relevant to allosteric modulation.…”