Inhibitor of the serine/threonine-protein kinase PAK4. Acts by binding PAK4 in a substrate-like manner, inhibiting the protein kinase activity. Interacts with PAK4. Enriched in the nervous system. During development, expressed in oligodendrocyte progenitor cells and in the proliferative neuronal progenitors in the developing cerebellum. In the embryonic brain, not expressed in immature newborn neurons, except for the cells residing in the marginal zone of the embryonic telencephalon. As brain development proceeds during the postnatal stage, expressed in some populations of immature neurons, including the neocortical pyramidal neurons, hippocampal pyramidal neurons and granule cells migrating in the cerebellar cortex. In the adult brain, expression is confined in terminally differentiated neurons in the restricted forebrain regions. The Inka box (also named iBox or inca box) binds and inhibits PAK4 by binding a substrate-like manner. Belongs to the INKA family.