Editors' ChoiceScaffolding

A Minimal Clustering Motif

Science's STKE  01 Jul 2003:
Vol. 2003, Issue 189, pp. tw251-TW251
DOI: 10.1126/stke.2003.189.tw251

Assembly of proteins in macromolecular complexes is critical for many signaling processes, including organization of the postsynaptic membrane proteins. Christopherson et al. investigated how PSD-95, a palmitoylated scaffolding protein of the membrane-associated guanylate kinase (MAGUK) family, promoted protein clustering. Using tagged versions of PSD-95 or fragments of PSD-95, they determined that the first 13 amino acids, which also include two palmitoylated cysteine residues, were necessary and sufficient to produce clustering of PSD-95 or chimeric proteins [attaching the 13 amino acids to green fluorescent protein (GFP) and maltose, for example]. Oligomerization was detected by coimmunoprecipitation and required palmitoylation, because 2-bromopalmitate, an inhibitor of the palmitate transferase, or mutation of the sequence to prevent palmitoylation blocked oligomerization. Other palmitoylated sequences, such as the one from GAP43, did not induce oligomerization of chimeric proteins or of PSD-95 when used in place of the PSD-95 native sequence. In cells cotransfected with PSD-95 and Kv1.4 K+ channels, only those channels that were oligomeric clustered with PSD-95 in membrane microdomains. When the channel subunits were fused into a single subunit, then the channels were diffusely expressed on the cell surface. Surprisingly, the GAP43-PSD-95 chimera that cannot homooligomerize was capable of stimulating clustering of the Kv1.4 subunits. Elimination of the PSD-95 N-terminal palmitoylation sequence and addition of a C-terminal prenylation sequence allowed PSD-95 to promote Kv1.4 clustering, but did not promote homomultimerization. These data identify a short, palmitoylation-dependent sequence that is sufficient for PSD-95 homomultimerization, but also show that homomultimerization is not necessary for PSD-95-mediated clustering of the Kv1.4 channels. Lipid modification is essential for clustering activity, and reversible palmitoylation may represent one model for assembly and disassembly of postsynaptic complexes during activity-dependent changes in synaptic structure.

K. S. Christopherson, N. T. Sweeney, S. E. Craven, R. Kang, A. E.-D. El-Husseini, D. S. Bredt, Lipid- and protein-mediated multimerization of PSD-95: Implications for receptor clustering and assembly of synaptic protein networks. J. Cell Sci. 116, 3213-3219 (2003). [Abstract] [Full Text]