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 Transport (in British English) or transportation (in American English) is the intentional movement of humans, animals, and goods from one location to another. Modes of transport include air, land (rail and road), water, cable, pipelines, and ...

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 Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

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 granule In cellular biology, stress granules are biomolecular condensates in the cytosol composed of proteins and RNA that assemble into 0.1–2 μm membraneless organelles when the cell is under stress. The mRNA molecules found in stress granules a ...

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

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 Importin subunit alpha-1 is a protein that in humans is encoded by the ''KPNA2'' gene. The import of proteins into the nucleus is a process that involves at least 2 steps. The first is an energy-independent docking of the protein to the nuclear ...

* KPNA3 *

KPNA4 Importin subunit alpha-3, also known as karyopherin subunit alpha-4, is a protein that in humans is encoded by the ''KPNA4'' gene. Function The nuclear import of karyophilic proteins is directed by short amino acid sequences termed nuclear loc ...

* KPNA5 *

KPNA6 Importin subunit alpha-7 is a protein that in humans is encoded by the ''KPNA6'' gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is ...

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 Exportin 1 (XPO1), also known as chromosomal region maintenance 1 (CRM1), is a eukaryotic protein that mediates the nuclear export of various proteins and RNAs. History XPO1 (CRM1) originally was identified in the fission yeast ''Schizosacchar ...

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