Karyopherins are

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s involved in transporting molecules between the

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...

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 Nucle ...

of a

eukaryotic cell Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacter ...

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

nuclear pore A nuclear pore is a part of a large complex of proteins, known as a nuclear pore complex that spans the nuclear envelope, which is the double membrane surrounding the eukaryotic cell nucleus. There are approximately 1,000 nuclear pore complexes ...

s which acts 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 cell's cytoplasm to the nucleus. It does so by binding to specific recognition sequences, called nuclear localization sequences (NLS). Importin has two subunits, import ...

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 (TCDB). Energy for transport is derived from the

Ran Ran, RaN and ran may refer to: Arts and entertainment * ''Ran'' (film), a 1985 film directed by Akira Kurosawa * "Ran" (song), a 2013 Japanese song by Luna Sea * '' Ran Online'', a 2004 MMORPG (massively multiplayer online role playing game) * ...

gradient. Upon stress, several karyopherins stop shuttling between the nucleus and the cytoplasm and are sequestered in

stress granule Stress granules are dense aggregations in the cytosol composed of proteins and RNAs that appear when the cell is under stress. The RNA molecules stored are stalled translation pre-initiation complexes: failed attempts to make protein from mRNA. St ...

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 in ...

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, import ...

is a variety of karyopherin that facilitates the transport of cargo proteins into the nucleus. First, it is binding

importin alpha 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, import ...

– another type of karyopherin that binds the

cargo protein Cargo consists of bulk goods conveyed by water, air, or land. In economics, freight is cargo that is transported at a freight rate for commercial gain. ''Cargo'' was originally a shipload but now covers all types of freight, including trans ...

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

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 and UBR5 E3 ubiquitin-protein ligase UBR5 is an enzyme that in humans is encoded by ...

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 Importin subunit alpha-4 also known as karyopherin subunit alpha-3 is a protein that in humans is encoded by the ''KPNA3'' gene. The transport of molecules between the nucleus and the cytoplasm in eukaryotic cells is mediated by the nuclear pore ...

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 loca ...

KPNA5 Importin subunit alpha-6 is a protein that in humans is encoded by the ''KPNA5'' gene. The transport of molecules between the nucleus and the cytoplasm in eukaryotic cells is mediated by the nuclear pore complex (NPC) which consists of 60-100 prot ...

KPNA6 Importin subunit alpha-7 is a protein that in humans is encoded by the ''KPNA6'' gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ...

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. ...

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 ''Schizosaccharom ...

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