Dual roles of the N‐terminal coiled‐coil domain of an Aplysia sec7 protein: homodimer formation and nuclear export

Cytohesin family proteins act as guanine nucleotide exchange factors ( GEF s) for the ADP ‐ribosylation factor family of small GTP ‐binding proteins. Aplysia Sec7 (ApSec7), a member of the cytohesin family in Aplysia, plays key roles in neurite outgrowth in Aplysia neurons. Although ApSec7 has a conserved coiled‐coil ( CC ) domain, its role was not clear. In this study, we found that the CC domain of ApSec7 and ARNO /cytohesin 2 are involved in homodimer formation, leading to efficient plasma membrane targeting of ApSec7 and ARNO /cytohesin 2 in HEK 293T cells. Therefore, deletion of the CC domain of ApSec7 and ARNO /cytohesin 2 may result in a loss of dimerization and reduce plasma membrane localization. In addition, the CC domains of ApSec7 and ARNO /cytohesin 2 have partially or fully CRM 1‐dependent nuclear export signals, respectively. Taken together, our results suggest that the CC domain of cytohesin family proteins, including ApSec7 and ARNO /cytohesin 2, has dual roles in intracellular targeting: increased plasma membrane targeting through homodimer formation and nuclear exclusion through either a CRM 1‐dependent or a CRM 1‐independent pathway.