Disordered Motifs and Domains in Cell Control
Poster Session II
26-POS
Board 2
Single-molecule Fluorescence Reveals How Dynamics within Cdk2/CyclinA-bound p27
Mediate Signal Transmission
Maksym Tsytlonok
1
, Hugo Sanabria
3
, Yuefeng Wang
2
, Cheon-Gil Park
2
, Suren Felekyan
3
,
Katherina Hemmen
3
, Peter Tompa
1
, Claus Seidel
3
, Richard Kriwacki
2
.
1
VIB Brussels, Brussels, Belgium,
2
St. Jude Children's Research Hospital, Memphis, TN,
USA,
3
Dusseldorf University, Dusseldorf, Germany.
In the classical structure-function paradigm the function of a protein is associated with its three-
dimensional structure. However, recent studies using single-molecule FRET, NMR and other
techniques have questioned the idea that proteins are static molecules. This phenomenon is
exacerbated especially in the proteins that are fully or partially unstructured, termed intrinsically
disordered proteins (IDPs). The intrinsic flexibility of IDPs affords functional advantages in
molecular recognition. One of the most prominent examples is the disordered polypeptide p27: It
is able to regulate eukaryotic cell division by interacting with a number of cyclin-dependent
kinase (Cdk)/cyclin complexes, as well as with other nuclear and cytoplasmic targets.
Phosphorylation of p27 by oncogenic kinases contributes to tumorigenesis in several human
cancers. The crystal structure of p27 bound to Cdk/Cyclin complex and ensemble measurements
provide molecular details of the specificity and the sequential induced-folding mechanism of this
interaction. However, the mechanistic details of the dynamic processes associated with the
phosphorylation of p27 required for the degradation of p27 are not completely understood. By
applying single-molecule fluorescence spectroscopy in combination with biochemical data, we
will provide a basis for understanding how dynamics within Cdk2/CyclinA-bound p27 mediate
signal transmission. Our results show that p27 exhibits dynamics in its bound conformation and
upon phosphorylation several domains are sequentially released. These observations explain the
mechanism of how intra- and inter-molecular phosphorylation of partially activated
Cdk2/CyclinA are regulated during the cell-cycle.
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