Interaction of spindle assembly factor TPX2 with importins-α/β inhibits protein phase separation.

TitleInteraction of spindle assembly factor TPX2 with importins-α/β inhibits protein phase separation.
Publication TypeJournal Article
Year of Publication2021
AuthorsSafari, MS, King, MR, Brangwynne, CP, Petry, S
JournalJ Biol Chem
Date Published2021 Sep
Keywordsalpha Karyopherins, beta Karyopherins, Cell Cycle Proteins, Chromatography, Gel, Humans, Microtubule-Associated Proteins, Microtubules, Nuclear Localization Signals, Nuclear Proteins, Protein Binding, Spindle Apparatus

<p>The microtubule-based mitotic spindle is responsible for equally partitioning the genome during each cell division, and its assembly is executed via several microtubule nucleation pathways. Targeting Protein for XKlp2 (TPX2) stimulates the branching microtubule nucleation pathway, where new microtubules are nucleated from preexisting ones within mitotic or meiotic spindles. TPX2, like other spindle assembly factors, is sequestered by binding to nuclear importins-α/β until the onset of mitosis, yet the molecular nature of this regulation remains unclear. Here we demonstrate that TPX2 interacts with importins-α/β with nanomolar affinity in a 1:1:1 monodispersed trimer. We also identify a new nuclear localization sequence in TPX2 that contributes to its high-affinity interaction with importin-α. In addition, we establish that TPX2 interacts with importin-β via dispersed, weak interactions. We show that interactions of both importin-α and -β with TPX2 inhibit its ability to undergo phase separation, which was recently shown to enhance the kinetics of branching microtubule nucleation. In summary, our study informs how importins regulate TPX2 to facilitate spindle assembly, and provides novel insight into the functional regulation of protein phase separation.</p>

Alternate JournalJ Biol Chem
PubMed ID34302807
PubMed Central IDPMC8390506
Grant List / HHMI / Howard Hughes Medical Institute / United States
T32 GM007388 / GM / NIGMS NIH HHS / United States