Karyopherins are
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
s involved in
transporting molecules between the
cytoplasm and the
nucleus of a
eukaryotic cell. The inside of the nucleus is called the karyoplasm (or nucleoplasm). Generally, karyopherin-mediated transport occurs through
nuclear pores which act as a gateway into and out of the nucleus. Most proteins require karyopherins to traverse the nuclear pore.
Karyopherins can act as ''
importins'' (i.e. helping proteins get into the nucleus) or ''exportins'' (i.e. helping proteins get out of the nucleus). They belong to the nuclear pore complex family in the
transporter classification database (TCDB). Energy for transport is derived from the
Ran gradient.
Upon stress, several karyopherins stop shuttling between the nucleus and the cytoplasm and are sequestered in
stress granules, cytoplasmic aggregates of
ribonucleoprotein complexes.
Importin beta
Importin beta is a variety of karyopherin that facilitates the transport of cargo proteins into the nucleus. First, it is binding
importin alpha – another type of karyopherin that binds the
cargo protein in the cytoplasm—before the cargo protein is imported into the nucleus through the
nuclear pore using energy derived from the
Ran gradient. Once inside the nucleus, the cargo dissociates from the karyopherins.
Importin beta can also carry proteins into the nucleus without the aid of the
importin alpha adapter protein.
[Poon, I. K. H. and D. A. Jans (2005). "Regulation of nuclear transport: Central role in development and transformation?" Traffic 6(3): 173-186.]
Human genes in the karyopherin family
*
KPNA1
*
KPNA2
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KPNA3
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KPNA4
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KPNA5
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KPNA6
*
KPNB1
*
CRM1
Additional images
Image:RanGTPcycle.png, The Ran-GTP cycle
References
External links
*
Illustrations at berkeley.edu
Karyopherin animationsKaryopherin illustrations3D electron microscopy structures of exportin from the EM Data Bank(EMDB)
Transport proteins
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