Cloning and characterization of AASPs: novel axon-associated SH3 binding-like proteins

Two cDNAs encoding closely related proteins were isolated from a crayfish nervous system lambdagtl0 cDNA library with a rat synapsin Ia cDNA probe. These proteins were expressed exclusively in neurons, were highly enriched in axons of the crayfish, and contained multiple, overlapping, putative Src homology 3 (SH3) binding sites. In concert with other proteins containing Src homology domains, SH3 binding proteins are thought to mediate protein-protein interactions in receptor signaling processes and with the cytoskeleton. We have named these proteins axon-associated SH3 binding-like proteins (AASPs). Except for these SH3 binding regions, which are also found in synapsins, AASPs were unlike any proteins in the database. AASPs were differentially expressed among motoneuron populations in crayfish and were found in growing axons and growth cones in culture. Affinity purified polyclonal antibodies to AASP-168 recognized immunoreactive proteins in rat and Xenopus, suggesting that AASPs may be conserved across species. Although the cellular function of AASPs is unclear at this time, they appear to be novel members of a neuron-specific SH3 binding protein family, which includes the synapsins.