Karyopherins and Nuclear actin transport

Although compartmentalization of a eukaryotic cell into the nucleus and cytoplasm has benefits, it further necessitates transport between the two compartments. Active transport between these two compartments requires metabolic energy and transporter proteins. Nuclear transporter receptors belong to the karyopherin super family and aid in the movement of cargo into (importers) or out of the nucleus (exporters) or are bidirectional. Presence of actin in nucleus and its nuclear trafficking remains intriguing due to its lack of nuclear import or export signals. Despite the fact that importin-9 and exportin-6 have been linked to nuclear import and export of actin respectively, the mechanistic details about actin-karyopherin interaction are not known yet. In this review, we compared the structural details of already available karyopherins and provide the initial structural prediction for exportin-6. The WH2 domain from diverse actin binding proteins display a similar architecture of N-terminal α helix followed by the LKKT(V) motif. A similar LKPS motif was identified near helix 14A of exportin-6, which might be the binding site for actin. Based on these predictions, we have postulated a mechanism of actin-karyopherin interaction.