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Nuclear Pore Complex under Karyopherin-Centric Control

저자:   업로드:2017-09-07  조회수:

    Although scientists appreciate that the nuclear pore complex (NPC) is more than a complex structure, and that it is, in fact, an intricate machine, they are still trying to work out all the mechanistic details. For example, they are looking for the interlocking gears that drive NPC functions, such as barrier selectivity, the transport of cargo complexes, and cargo release from cargo complexes, once the cargo has been imported into the nucleus.

    New research on nuclear transport regulation might overthrow established models, which tend to emphasize the role of the nuclear pore itself, rather than its accessories, which include protein factors called karyopherins (Kaps). Indeed, one new study, out of the University of Basel, suggests that Kaps known as importin alpha (or Kapα) and importin beta (or Kapβ) are at the center of NPC control.

    In contrast to prevailing views, a research team led by Roderick Lim, Ph.D., Argovia Professor at the Biozentrum and the Swiss Nanoscience Institute of the University of Basel, has now demonstrated that the NPC does not work like a simple filter that regulates the nuclear transport process. Rather, Kapα and Kapβ cooperate to continuously open and close the pore like a revolving door.

    Details appeared in the Journal of Cell Biology, in an article entitled “Karyopherins Regulate Nuclear Pore Complex Barrier and Transport Function.” The article focuses on how nucleocytoplasmic transport is sustained by Kaps and a Ran guanosine triphosphate (RanGTP) gradient that imports nuclear localization signal (NLS)–specific cargoes (NLS-cargoes) into the nucleus.

    “Kapα facilitates Kapα turnover and occupancy at the NPC in a RanGTP-dependent manner that is directly coupled to NLS-cargo release and NPC barrier function,” wrote the article’s authors. “This is underpinned by the binding affinity of Kapβ1 to phenylalanine–glycine nucleoporins (FG Nups), which is comparable with RanGTP·Kapβ1, but stronger for Kapα·Kapβ1.”

    For a long time, scientists have reasoned that a molecular filter within the NPC prevents or enables the passage of molecules into the nucleus. Prof. Lim's current study now shows that this filter alone is not sufficient for barrier function but provides only the basic infrastructure for establishing one. Instead, cargo-carrying importins function as bona fide components that regulate the NPC transport barrier.

    Prof. Lim and colleagues show how the shuttling of Kap importins is coupled to their barrier function—Kapβ1 promotes cargo access into the pore, whereas Kapα determines the cargo that can enter the nucle

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