Karyopharin Beta 2
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 protein into the nucleus through interactions with nucleoporins, which are proteins of the nucleopore complex (NPC). One might overlook the significance of this protein but 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 KAPβ is composed of 20 antiparallel helices called HEAT repeats. These HEAT repeats contribute to kapβ2’s large superhelical 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.
