Tetrameric Hub Structure of Postsynaptic Scaffolding Protein Homer

Abstract

Homer is a crucial postsynaptic scaffolding protein involved in both maintenance and activity-induced plasticity of the synapse. However, its quaternary structure has yet to be determined. We conducted a series of biophysical experiments that provide the first evidence that Homer forms a tetramer via its coiled-coil domain, in which all subunits are aligned in parallel orientation. To test the importance of the tetrameric structure for functionality, we engineered dimeric and tetrameric Homer by deleting a part of coiled-coil domain or replacing it with artificially engineered dimeric or tetrameric coiled-coil domain from a yeast protein. The structure-activity relationship was determined by assaying cocluster formation with its ligand in heterologous cells, distribution in dendritic spines, and turnover rate of protein exist in dendritic spines. Our results provide the first insight into the structure of native Homer protein as a tetramer and the functional significance conferred by that structure.

Homer proteins in Ca2+ signaling by excitable and non-excitable cells

“…In this expression system, H1b/c, but not H1a, increases the localization of mGluRs in the plasma membrane [11]. The C terminal portion of the coiled-coil domain (the CC2 region) mediates the subcellular localization of Homer itself and plays a role in clustering of mGluRs [7].…”

“…Homer 2 and 3 are identical in domain structure to H1b. The N terminus EVH1 domain of the different Homers displays 60-70% sequence conservation, whereas the C terminus coiled-coil domains have only about 20% sequence identity [7]. A recent structural analysis reveals that the long Homers form an elongated tetramer via their coiled-coil domains [7].…”

“…The N terminus EVH1 domain of the different Homers displays 60-70% sequence conservation, whereas the C terminus coiled-coil domains have only about 20% sequence identity [7]. A recent structural analysis reveals that the long Homers form an elongated tetramer via their coiled-coil domains [7]. The tetrameric Homer can form a lattice with other scaffolds to bind Ca 2+ signaling proteins in cellular microdomains [3,5,[8][9][10].…”

Phosphorylation of Homer3 by Calcium/Calmodulin-Dependent Kinase II Regulates a Coupling State of Its Target Molecules in Purkinje Cells

“…Is the phosphorylationinduced reduction in affinity sufficient for the Homer3 dissociation in vivo? A recent report by Hayashi et al (2006) demonstrated that tetramer formation of Homer protein is necessary for both coclustering with its ligand and synaptic targeting. Thus, one possibility is that phosphorylation at the linker region of Homer3 induces a conformational change that results in breaking up of the tetramer.…”

“…The long-form Homer proteins, Homer1b/c, Homer2, and Homer3, have the C-terminal coiledcoil region, which is responsible for their tetramer formation and enable to link target molecules at specific cellular regions, such as at excitatory postsynaptic sites (Hayashi et al, 2006). In contrast, Homer1a, which shows synaptic activity-dependent expression and fails to form tetramer attributable to lacking a coiled-coil region, is thought to function as a natural dominant negative to break clustering and/or linking target molecules (Brakeman et al, 1997;Kato et al, 1998;Kammermeier and Worley, 2007).…”