Acts as a specific nuclear import carrier for HSP70 proteins following heat-shock stress: acts by mediating the nucleoporin-dependent translocation of ATP-bound HSP70 proteins into the nucleus. HSP70 proteins import is required to protect cells from heat shock damages. Does not translocate ADP-bound HSP70 proteins into the nucleus (By similarity). May also be indirectly required for organization and/or function of the secretory apparatus in Clara cells in lung. Forms an asymmetric homodimer; required for binding and nuclear import of HSP70 proteins. Interacts with ATP-bound HSP70 proteins. Interacts with NUP62 and NUP153 (via F-X-F-G repeats). Interacts with HSPA8. Expressed in the central white matter of newborn and adult brain, particularly in regions where oligodendrocytes are generated (PubMed:26545878). During late gestation, it is expressed in lung epithelial cells, whereas perinatal expression is restricted to the bronchiolar epithelium. Mice display severe emphysematous enlargement of the distal respiratory sacs at birth. Clara cell display enlargement and disorganization of the Golgi complex and formation of aberrant vesicular structures. Belongs to the OPI10 family.