Disordered Motifs and Domains in Cell Control
Poster Session I
18-POS
Board 18
Multivalent Interaction of Higher-order Oligomers of SPOP with the Transcriptional
Activator Gli3
Jihun Lee
, Melissa R. Marzahn, Wendy K. Pierce, Tanja Mittag.
St. Jude Children's Research Hospital, Memphis, TN, USA.
Multivalent interactions, in which each binding partner has multiple binding sites or binding
motifs for the other protein, can lead to the assembly of large higher-order complexes allowing
for subcellular organization. Speckle-type POZ protein (SPOP), recently identified as a novel
tumor suppressor, localizes to nuclear puncta and is a substrate adaptor of a cullin3-RING
ubiquitin ligase (CRL). It recruits substrates to the CRL and promotes their ubiquitination and
downstream degradation. SPOP self-associates into large higher-order homo-oligomers through
its two independent oligomerization domains, rendering it multivalent for substrates. Some
SPOP substrates, such as Gli3, reportedly harbor many SPOP binding motifs. Here, we identified
SPOP binding motifs in Gli3 and determined that SPOP self-associates indefinitely through an
isodesmic self-association mechanism. Using a variety of biophysical methods including
dynamic light scattering (DLS), composition gradient multi-angle light scattering (CG-MALS),
biolayer interferometry (BLI) and cellular assays we studied the multivalent interaction between
SPOP and Gli3. We investigated self-association and substrate binding of SPOP mutants found
in cancers comparing physiological and pathological SPOP properties. We determined factors
promoting SPOP localization in nuclear punctate structures. The formation of higher-order
complexes may result in subcellular organization but may also lead to activity enhancement
through high local concentrations of components, and ultrasensitive regulation of signaling
pathways.
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