Abbreviations used in this paper: CSP, cysteine string protein; EAAT4, excitatory amino acid transporter 4; Fas II, fasciclin II; FSPAM, fly spectrin American mutant; FSPGM, fly spectrin German mutant; FSPWT, fly spectrin wild type; hSPAM, human spectrin American mutation; hSPGM, human spectrin German mutation; hSPWT, human spectrin wild type; NMJ, neuromuscular junction; n-syb, neuronal synaptobrevin; RIPA, radio immunoprecipitation assay; SCA5, spinocerebellar ataxia type 5; syt, synaptotagmin.