The C-terminal t peptide (40 residues) of vertebrate acetylcholinesterase (AChE) T subunits possesses a series of seven conserved aromatic residues and forms an amphiphilic α-helix; it allows the formation of homo-oligomers (monomers, dimers and tetramers) and heteromeric associations with the anchoring proteins, ColQ and PRiMA, which contain a proline-rich motif (PRAD). We analyzed the influence of mutations in the t peptide of Torpedo AChET on oligomerization and secretion. Charged residues influenced the distribution of homo-oligomers but had little effect on the heteromeric association with QN, a PRAD-containing N-terminal fragment of ColQ. The formation of homo-tetramers and QN-linked tetramers required a central core of four aromatic residues and a peptide segment extending to residue 31; the last nine residues (32–40) were not necessary, although the formation of disulfide bonds by cysteine C37 stabilized T4 and T4–QN tetramers. The last two residues of the t peptide (EL) induced a partial intracellular retention; replacement of the C-terminal CAEL tetrapeptide by KDEL did not prevent tetramerization and heteromeric association with QN, indicating that these associations take place in the endoplasmic reticulum. Mutations that disorganize the α-helical structure of the t peptide were found to enhance degradation. Co-expression with QN generally increased secretion, mostly as T4–QN complexes, but reduced it for some mutants. Thus, mutations in this small, autonomous interaction domain bring information on the features that determine oligomeric associations of AChET subunits and the choice between secretion and degradation.