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 The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

and the nucleus of a

eukaryotic cell The eukaryotes ( ) constitute the domain of Eukaryota or Eukarya, organisms whose cells have a membrane-bound nucleus. All animals, plants, fungi, seaweeds, and many unicellular organisms are eukaryotes. They constitute a major group of Out ...

. The inside of the nucleus is called the karyoplasm (or nucleoplasm). Generally, karyopherin-mediated transport occurs through

nuclear pore The nuclear pore complex (NPC), is a large protein complex giving rise to the nuclear pore. A great number of nuclear pores are studded throughout the nuclear envelope that surrounds the eukaryote cell nucleus. The pores enable the nuclear tran ...

s which act as a gateway into and out of the nucleus. Most proteins require karyopherins to traverse the nuclear pore. Karyopherins can act as ''

importin Importin is a type of karyopherin that transports protein molecules from the Eukaryotic Cell, cell's cytoplasm to the cell nucleus, nucleus. It does so by binding to specific recognition sequences, called nuclear localization sequences (NLS). I ...

s'' (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 The Transporter Classification Database (or TCDB) is an International Union of Biochemistry and Molecular Biology (IUBMB)-approved classification system for membrane transport proteins, including ion channels. Classification The upper level of cla ...

(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 Nucleoproteins are proteins conjugated with nucleic acids (either DNA or RNA). Typical nucleoproteins include ribosomes, nucleosomes and viral nucleocapsid proteins. Structures Nucleoproteins tend to be positively charged, facilitating inter ...

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

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 Importin subunit alpha-5 is a protein that in humans is encoded by the ''KPNA1'' gene. Interactions Importin subunit alpha-5 has been shown to interact with KPNB1 Importin subunit beta-1 is a protein that in humans is encoded by the ''KPNB1'' ...

* KPNA2 * KPNA3 * KPNA4 * KPNA5 * KPNA6 *

KPNB1 Importin subunit beta-1 is a protein that in humans is encoded by the ''KPNB1'' gene. Function Nucleocytoplasmic transport, a signal- and energy-dependent process, takes place through nuclear pore complexes embedded in the nuclear envelope. T ...

* CRM1

Additional images

Image:RanGTPcycle.png, The Ran-GTP cycle

References

External links

*
Illustrations at berkeley.edu

Karyopherin animations

Karyopherin illustrations

3D electron microscopy structures of exportin from the EM Data Bank(EMDB)
Transport proteins {{protein-stub