title: Molecular basis for the recognition of a nonclassical nuclear localization signal by importin beta.
abstract: Nuclear import of proteins containing a classical nuclear localization signal (NLS) involves NLS recognition by importin alpha, which associates with importin beta via the IBB domain. Other proteins, including parathyroid hormone-related protein (PTHrP), are imported into the nucleus by direct interaction with importin beta. We solved the crystal structure of a fragment of importin beta-1 (1-485) bound to the nonclassical NLS of PTHrP. The structure reveals a second extended cargo binding site on importin beta distinct from the IBB domain binding site. Using a permeabilized cell import assay we demonstrate that importin beta (1-485) can import PTHrP-coupled cargo in a Ran-dependent manner. We propose that this region contains a prototypical nuclear import receptor domain, which could have evolved into the modern importin beta superfamily.
authors.affiliation: Departments of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors.forename: Gino
authors.initials: G
authors.lastname: Cingolani
authors.forename: Janna
authors.initials: J
authors.lastname: Bednenko
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Gillespie
authors.forename: Larry
authors.initials: L
authors.lastname: Gerace
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000595:Amino Acid Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism*; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments / Q000737:chemistry; D036361:Peptide Hormones / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D015398:Signal Transduction; D055672:Static Electricity; D013499:Surface Properties; D028961:beta Karyopherins / Q000737:chemistry / Q000378:metabolism*
chemical_list: C470121:PTHLH protein, human; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments; D036361:Peptide Hormones; D011994:Recombinant Proteins; D028961:beta Karyopherins