Structural basis for substrate recognition and dissociation by human transportin 1

Area of Science:

• Molecular Biology
• Structural Biology
• Cell Biology

Background:

• Transportin 1 (Trn1) is a key nuclear transport receptor.
• It facilitates the import of proteins into the nucleus by recognizing nuclear localization signals (NLSs).
• Understanding Trn1's mechanism is crucial for nuclear import pathways.

Purpose of the Study:

• To elucidate the structural basis of substrate recognition and dissociation by Transportin 1.
• To investigate the role of Trn1's binding sites and conformational changes during nuclear import.

Main Methods:

• X-ray crystallography was used to determine four crystal structures.
• Structures were obtained for substrate-free human Trn1 and Trn1 complexed with three different NLSs (hnRNP D, JKTBP, TAP).

Main Results:

• Human Trn1 possesses two distinct NLS binding sites: a high-affinity site A and a low-affinity site B.
• NLS interaction at site B is critical for modulating the overall binding affinity of Trn1.
• Trn1 first recognizes NLSs at site A, inducing a conformational change at site B for subsequent interaction.
• A characteristic long flexible loop of Trn1 interacts with site B, facilitating the displacement of transport substrates within the nucleus.

Conclusions:

• The study reveals a dual-site binding mechanism for NLS recognition by Trn1.
• Conformational dynamics involving site B and a flexible loop are essential for Trn1's function in nuclear import and substrate release.