The adapter importin‐α provides flexible control of nuclear import at the expense of efficiency

Open Access
Publisher Website
Google Scholar
Abstract
Although there exists a large family of nuclear transport receptors (Karyopherins), the majority of known import cargoes use an adapter protein, Importin‐α (Impα), which links the cargo to a karyopherin, Importin‐β (Impβ). The reason for the existence of transport adapters is unknown. One hypothesis is that, as Impα re‐export is coupled to GTP hydrolysis, it can drive a higher concentration of nuclear cargo than could be achieved by direct cargo binding to Importin‐β. However, computer simulations predicted the opposite outcome, and showed that direct transport is faster than adapter‐mediated transport. These predictions were validated experimentally. The data, together with previous analyses of nuclear protein import, suggest that the use of adapters such as importin‐α provides the cell with increased dynamic range for control of nuclear import rates, but at the expense of efficiency. Mol Syst Biol. 3: 118