The local mechanostructural properties of protein cargoes regulate nucleocytoplasmic transport.

The nuclear pore complex regulates nucleocytoplasmic transport. It was recently shown that the global mechanical stability of proteins regulates their nuclear import rate. On the basis of these findings, we hypothesize that the main principles governing protein translocation through narrow biological pores-in which locally unstructured and unfolded regions determine cargo orientation and translocation kinetics-can help rationalize protein trafficking across the nuclear pore complex. Inspired by single-molecule studies showing that proteins exhibit different mechanical stability when pulled from different termini, here we show that the rate of both nuclear import and export is enhanced when the translocating protein is threaded through the nuclear pore from the specific region exhibiting lower local nanomechanical stability and increased structural disorder. We demonstrate this for a range of model proteins with different folds and stabilities by combining single-molecule magnetic tweezers with single-cell optogenetic experiments, complemented by steered molecular dynamics simulations and biochemical binding assays. Our bioinformatics survey then shows that in human transcription factors, the termini containing the nuclear localization signal sequence exhibit a higher degree of structural disorder. We propose that protein orientation might offer an additional layer of structural and mechanical control of the kinetics of nuclear transport.