Structural basis for the specificity of bipartite nuclear localization sequence binding by importin-alpha

Area of Science:

• Molecular Biology
• Structural Biology
• Cell Biology

Background:

• Importin-alpha acts as the primary receptor for nuclear import, recognizing proteins with basic nuclear localization sequences (NLSs).
• Bipartite NLSs feature two basic residue clusters separated by linkers of varying lengths and sequences.
• Understanding the structural basis of NLS recognition by importin-alpha is crucial for elucidating nuclear transport mechanisms.

Purpose of the Study:

• To investigate the structural mechanisms underlying importin-alpha's recognition of diverse bipartite NLSs.
• To determine how variations in linker sequences and lengths affect NLS binding and importin-alpha interaction.

Main Methods:

• Co-crystallization of a non-autoinhibited mouse importin-alpha with synthetic peptides representing bipartite NLSs from human retinoblastoma protein and Xenopus laevis phosphoprotein N1N2.
• X-ray crystallography to determine the high-resolution structures of importin-alpha-NLS peptide complexes.

Main Results:

• Both basic clusters within the bipartite NLSs interact with importin-alpha in a similar manner.
• The linker regions exhibit distinct conformations and form specific contacts with the importin-alpha receptor.
• Structural data reveal insights into the specificity of NLS binding by importin-alpha.

Conclusions:

• Importin-alpha exhibits a flexible binding mechanism accommodating diverse bipartite NLS structures.
• The findings facilitate an improved definition of the consensus sequence for basic/bipartite NLSs (KRX10-12KRRK).
• This improved consensus sequence can aid in the identification of novel nuclear proteins involved in nucleocytoplasmic transport.