Sandbox 130: Difference between revisions
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==Karyopherin β2== | ==Karyopherin β2== | ||
Karyopherinβ is a group of proteins that is composed of both importins and exportins. Importins are proteins that carry cargos into the nucleus while exportins serve the opposite function. As of today, twenty different Kapβs have been identified. Each of these Kapβs is capable of recognizing and transporting a specific group of cargos. In order to bind to its cargo a Kapβ has to recognize a Nuclear Localization or Export Signal (NLS or NES). | |||
Karyopherin beta 2 (kapβ2) is an importin that transports various cargo proteininto the nucleus through interactions with nucleoporins, which are proteins of thenuclear pore complex (NPC). The NPC is a large structure consisting of 456 constituent binding proteins called nucleoporins (Nups). 1 Movement through the NPC is facilitated transport that relies on interaction with specific Nups. Importins and exportins are proteins that aid this facilitated transport by both binding to a specific cargo to be transported and interacting with specific Nups located in the central channel of the NPC.2 One might overlook the significance of this protein but actually plays a crucial role in the human body by mediating transport ofRNA- binding proteins involved in transcription, RNA processing, RNA transportand translation. The structure of KAPβ is composed of 20 antiparallel helicescalled HEAT repeats. These HEAT repeats contribute to kapβ2’s largesuperhelical shape. That form two arches: one at the N-terminal and the other at the C- terminal. Through recognition of a nuclear localization signal (NLS) located on its cargo, kapβ2 binds to its cargo via its C-terminal arch. Release of the cargo is mediated by RanGTP, which once bound, modifies the shape of kapβ2. Release of the cargo is mediated once contact occurs between RanGTP and N-terminal arch of Kapβ2. | |||
In eukaryotes, proteins must be transported in and out of the nucleus. This nucleocytoplasmic transport of proteins across the nuclear envelope must occur through the gateway of the NPC. | |||
An importin, such as Kapβ2, binds to a specific cargo by recognition of an NLS and carries the cargo through the NPC by interacting with intrinsically disordered Nups called FG-Nups. FG-Nups are repeats of phenylalanine and glycine. These unstructured FG-Nups form a low-density cloud within the central channel extending from the cytoplasm to the nucleoplasm. The cloud acts as an effective exclusion filter for those particles that do not contain FG repeat binding sites. This is referred to as the zone of selectivity. | |||