Structural basis for Nup2p function in cargo release and karyopherin recycling in nuclear import

Area of Science:

• Molecular Biology
• Cell Biology
• Structural Biology

Background:

• The yeast nucleoporin Nup2p plays a crucial role in nuclear pore complex function.
• Nup2p is essential for efficient nuclear protein import and export mediated by importin-alpha:beta.
• Specific Nup2p residues (1-51) are critical for binding Kap60p and in vivo function.

Purpose of the Study:

• To elucidate the structural basis of the interaction between Nup2p and Kap60p.
• To understand the role of Nup2p in nuclear transport regulation.
• To investigate how Nup2p influences nuclear import termination and importin recycling.

Main Methods:

• X-ray crystallography to determine the 2.6 Å resolution structure of the Nup2p-Kap60p complex.
• Biochemical assays to analyze binding affinities and release kinetics.
• In vivo functional studies of Nup2p.

Main Results:

• The crystal structure reveals Nup2p binding along the concave groove of Kap60p's armadillo repeat domain.
• Nup2p's interaction interface with Kap60p differs from, but overlaps with, nuclear localization signal (NLS) binding sites.
• Nup2p binds Kap60p more strongly than NLSs and accelerates NLS release, while its own release requires Cse1p:RanGTP and the importin-beta binding (IBB) domain.

Conclusions:

• Nup2p acts as a key regulator of nuclear trafficking by coordinating import termination and importin recycling.
• The structural insights explain Nup2p's function in accelerating nuclear transport processes.
• Nup2p enhances overall nuclear transport efficiency through a concerted mechanism involving importin recycling.