Sandbox 125
From Proteopedia
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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 line the passageway of the NPC and contain 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. | 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 line the passageway of the NPC and contain 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. | ||
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Revision as of 17:16, 31 July 2013
Introduction
Karyopherin beta 2 (Kapβ2) is an importin that transports various cargo proteins into the nucleus through interactions with nucleoporins, which are proteins of the nuclear pore complex (NPC). One might overlook the significance of this protein but it actually plays a crucial role in the human body by mediating transport of RNA-binding proteins involved in transcription, RNA processing, RNA transport and translation. The structure of Kapβ2 is composed of 20 antiparallel helices called HEAT repeats. These HEAT repeats contribute to Kapβ2’s large superhelical shape. The protein is shown to 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, leads to a large movement of the 62-residue heat repeat 8 loop into the C-terminal arch. This conformational change results in the dissociation of the cargo as the b2 loop binds the NLS binding site.
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