Zinedin, SG2NA, and Striatin Are Calmodulin-binding, WD Repeat Proteins Principally Expressed in the Brain

Abstract

Striatin is an intracellular protein characterized by four protein-protein interaction domains, a caveolinbinding motif, a coiled-coil structure, a calmodulinbinding domain, and a WD repeat domain, suggesting that it is a signaling or a scaffold protein. Down-regulation of striatin, which is expressed in a few subsets of neurons, impairs the growth of dendrites as well as rat locomotor activity (Bartoli, M., Ternaux, J. P., Forni, C., Portalier, P., Salin, P., Amalric, M., and Monneron, A. (1999) J. Neurobiol. 40, 234 -243). Zinedin, a "novel" protein described here, and SG2NA share with striatin identical protein-protein interaction domains and the same overall domain structure. A phylogenetic analysis supports the hypothesis that they constitute a multigenic family deriving from an ancestral gene. DNA probes and antibodies raised against specific domains of each protein showed that zinedin is mainly expressed in the central nervous system, whereas SG2NA, of more widespread occurrence, is mainly expressed in the brain and muscle. All three proteins are both cytosolic and membrane-bound. All three bind calmodulin in the presence of Ca 2؉ . In rat brain, SG2NA and striatin are generally not found in the same neurons. Both localize to the soma and dendrites, suggesting that they share a similar type of addressing and closely related functions.Striatin is an intracellular protein mostly present in neurons of mammalian basal ganglia and cranial and spinal motor nuclei (1, 2). Electron microscopy showed that it is present in the somato-dendritic compartment of neurons, especially in dendritic spines (1). Brain fractionation shows that striatin is both cytosolic and associated with membranes. This multimodular protein possesses, from the N to the C terminus, four domains mediating protein-protein interactions: a caveolinbinding domain (aa 1 55-63) (3), a putative coiled-coil structure (aa 70 -116), a Ca 2ϩ -calmodulin (CaM)-binding domain (aa 149 -166) (4),and a WD repeat domain (aa 419 -780). The WD repeat family is composed of homologous, structurally related, but functionally diverse proteins able to organize multiple simultaneous or consecutive protein-protein interactions (5). The richness of striatin in domains mediating protein-protein interactions suggests that striatin is both a signaling protein and a multimodular platform protein. A study aimed at elucidating the function of striatin revealed two sets of data demonstrating its central role both in embryonic neurons and in adult brain (6). On the one hand, we showed that the expression of striatin is essential for the maintenance and growth of dendrites in rat embryonic motoneurons in culture. On the other hand, we showed that striatin is involved in the control of motor function in adult rats. Albeit a quantitatively minor protein, striatin thus appears to play major cellular and physiological roles.We have previously reported that the sequence of SG2NA, a 713 aa, supposedly nuclear protein discovered by Muro et al. (7), is 80% similar to and 66% identical...

Molecular Cloning and Characterization of Phocein, a Protein Found from the Golgi Complex to Dendritic Spines

“…Phocein was wholly solubilized from a 100,000 ϫ g pellet using nonionic detergents such as Lubrol-PX or zwitterionic detergents such as 3-([3-cholamidopropyl]dimethylammonio)-2-hydroxy-1-propanesulfonate. Striatin and the other proteins of its family, zinedin and SG2NA, behave in the same way (Castets et al, 1996(Castets et al, , 2000Bartoli et al, 1998).…”

“…Validation of the interaction between phocein and striatin by in vitro experiments was straightforward. The respective interactions of phocein with SG2NA and zinedin, which belong to the striatin family (Castets et al, 2000), were also demonstrated.…”

“…The proteins belonging to the striatin family are identically distributed (Castets et al, 2000). Because the sequence of phocein lacks a region that could account for a transmembrane segment, as well as properly located motifs required for prenylation and myristoylation, phocein is likely to be associated with membranes through its interaction with striatin, zinedin, and SG2NA.…”

“…For coimmunoprecipitation assays, batches of 200 l of a 10% suspension of washed Pansorbin cells preincubated in 1% BSAcontaining Tris saline buffer (TBS buffer; 50 mM Tris-HCl, pH 7.4, and 150 mM NaCl) were incubated with 140 g of rabbit preimmune immunoglobulins or affinity-purified anti-phocein, anti-striatin, anti-SG2NA, and anti-zinedin antibodies, in the presence of 0.1% BSA (Castets et al, 2000) for at least 4 h at 4°C with gentle agitation. The Pansorbin cells were washed in TBS several times.…”

“…Because we recently showed that two proteins, SG2NA and zinedin, share with striatin identical proteinprotein association modules (Castets et al, 2000), we looked for their possible interaction with phocein, which, indeed, was verified by in vitro experiments.…”