SPAR2, a novel SPAR‐related protein with GAP activity for Rap1 and Rap2

Abstract

Spine‐associated RapGAP 2 (SPAR2) is a novel GTPase activating protein (GAP) for the small GTPase Rap that shows significant sequence homology to SPAR, a synaptic RapGAP that was reported to regulate spine morphology in hippocampal neurons. SPAR2, like SPAR, interacts with the recently described synaptic scaffolding protein ProSAP‐interacting protein (ProSAPiP), which in turn binds to the PDZ domain of ProSAP/Shank post‐synaptic density proteins. In subcellular fractionation experiments, SPAR2 is enriched in synaptosomes and post‐synaptic density fractions indicating that it is a synaptic protein. Furthermore, we could show using in vitro GAP assays that SPAR2 has GAP activity for Rap1 and Rap2. Expression in COS‐7 cells, however, revealed different actin‐binding properties of SPAR2 and SPAR. Additionally, over‐expression of SPAR2 in cultured hippocampal neurons did not affect spine morphology as it was reported for SPAR. In situ hybridization studies also revealed a differential tissue distribution of SPAR and SPAR2 with SPAR2 transcripts being mainly expressed in cerebellar and hippocampal granule cells. Moreover, in the cerebellum SPAR2 is developmentally regulated with a peak of expression around the period of synapse formation. Our results imply that SPAR2 is a new RapGAP with specific functions in cerebellar and hippocampal granule cells.

Synaptic Cross-talk between N-Methyl-d-aspartate Receptors and LAPSER1-β-Catenin at Excitatory Synapses

“…Fez1 domains are approximately 200 aa long and were found to specifically interact with the C termini of actin binding SPAR molecules (30) that localize at PSDs. It seems that this interaction is secured by redundant short interaction motifs because we found that even partial SPAR C-terminal sequences are efficiently bound to the LAPSER1 Fez1 domain.…”

“…E, to determine the interaction partner of the Fez1 domain, we performed a yeast two-hybrid screen employing the Fez1 domain as bait. To our surprise all 11 positive clones were coding for members of the SPAR family of proteins (30). The shortest prey clone was only ϳ200 aa long, indicating that the very C-terminal part contains the interaction motif.…”

“…To further characterize the functional role of the highly conserved Fez1 domain, we performed a yeast two-hybrid screen using the Fez1 domain as bait. This screen yielded several independent clones (n ϭ 11) that were all coding for partial C-terminal sequences of members of the SPAR family of proteins (30). Eight clones were coding for SPAR1, three were cod-ing for SPAR2, and none were coding for SPAR3.…”

A comparison of the synaptic proteome in human chronic schizophrenia and rat ketamine psychosis suggest that prohibitin is involved in the synaptic pathology of schizophrenia

“…37,38 Neurons were transfected at DIV7 and fixed with 4% paraformaldehyde (PFA) at DIV21. Stainings with synaptic and dendritic markers were performed as described above.…”

An Epha4/Sipa1l3/Wnt pathway regulates eye development and lens maturation

“…All Sipa family members share common domains, namely an N-terminal RapGAP domain (Rap-GTPase activating domain), a PDZ domain and a Cterminal coiled-coil domain that was found to harbor a leucine zipper (Wendholt et al, 2006). So far, Sipa1l1-3 have been analyzed mainly with respect to their synaptic function in the central nervous system (Dolnik et al, 2016;Pak et al, 2001;Spilker et al, 2008).…”