Palmitoylation regulates glutamate receptor distributions in postsynaptic densities through control of PSD95 conformation and orientation
2016-08,
Jeyifous, Okunola,
Lin, Eric I.,
Chen, Xiaobing,
Antinone, Sarah E.,
Mastro, Ryan,
Drisdel, Renaldo,
Reese, Thomas S.,
Green, William N.
PSD95 and SAP97 are homologous scaffold proteins with different
N-terminal domains, possessing either a palmitoylation site
(PSD95) or an L27 domain (SAP97). Here, we measured PSD95
and SAP97 conformation in vitro and in postsynaptic densities
(PSDs) using FRET and electron microscopy, and examined how
conformation regulated interactions with AMPA-type and NMDAtype
glutamate receptors (AMPARs/NMDARs). Palmitoylation of
PSD95 changed its conformation from a compact to an extended
configuration. PSD95 associated with AMPARs (via TARP subunits)
or NMDARs (via GluN2B subunits) only in its palmitoylated and
extended conformation. In contrast, SAP97 in its extended conformation
associates with NMDARs but not with AMPARs. Within
PSDs, PSD95 and SAP97 were largely in the extended conformation,
but had different orientations. PSD95 oriented perpendicular
to the PSD membrane, with its palmitoylated, N-terminal domain
at the membrane. SAP97 oriented parallel to the PSD membrane,
likely as a dimer through interactions of its N-terminal, L27 domain.
Changing PSD95 palmitoylation in PSDs altered PSD95 and AMPAR
levels but did not affect NMDAR levels. These results indicate that
in PSDs, PSD95 palmitoylation, conformation and its interactions
are dynamic when associated with AMPARs, and more stable when
associated with NMDARs. Altogether, our results are consistent
with differential regulation of PSD95 palmitoylation in PSDs resulting
from the clustering of palmitoylating and depalmitoylating enzymes
into AMPAR nanodomains segregated away from NMDAR
nanodomains.