Structural basis for PP2A-mediated regulation of accurate chromosome segregation
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Sotelo ParrillaP_2023.pdf (48.70Mb)
Date
12/07/2023Item status
Restricted AccessEmbargo end date
12/07/2024Author
Sotelo Parrilla, Paula
Metadata
Abstract
The dynamic crosstalk between kinases and phosphatases is essential to ensure faithful
mitosis. Protein phosphatases PP2A(B55) and PP2A(B56), and the Chromosomal
Passenger Complex -CPC, containing Aurora B kinase-, establish a signalling network that
controls sister chromatid cohesion, kinetochore-microtubule attachments, and timely
chromosome segregation. PP2A(B56), together with Shugoshin1 (Sgo1), opposes Aurora B
during early mitosis to protect cohesin from being disassembled at the inner centromere.
PP2A(B56) and Aurora B also act antagonistically in controlling the processes of error
correction and activation of the Spindle Assembly Checkpoint, both of which are essential to
achieve chromosome biorientation. PP2A(B55) is the master regulator of mitotic exit, as it
triggers late mitotic events by counteracting Cdk1 activity.
Combining biochemistry, structural biology and biophysics, my work sheds light into the
mechanistic basis of how PP2A regulates these key mitotic events through its interaction
with Shugoshin1, the Chromosomal Passenger Complex and the Ska complex.
Recent studies have shown that individual PP2A(B56) isoforms might have differential roles
during mitosis. Nevertheless, the structural and functional basis of this isoform specificity
and how it affects Sgo1 function remain unclear. In my thesis, I have explored the intricacies
of PP2A(B56)-Sgo1 interactions and have discovered that Sgo1 binds PP2A(B56) in a B56-
isoform-dependent manner. Our ongoing work hints that this specificity is mediated by
dynamic interactions between Sgo1 and the B56 subunits, and aims to decipher the
functional contribution of these interactions in achieving faithful chromosome segregation
My work also unveils a novel interaction between PP2A(B56) and the CPC. Structural
analysis of this complex shows that Borealin – one of the components of the CPC – contains
a short linear motif that binds PP2A(B56) via the LxxIxE-binding pocket of B56. This highly
conserved pocket is key for the recognition of PP2A(B56) interactors, and it is heavily
involved in the regulation of PP2A activity and localisation during mitosis. The importance of
this interaction in PP2A(B56) and/or CPC localisation and function in vivo is an outstanding
question that our ongoing research aims to resolve.
Recent studies suggested that PP2A(B55) might interact with the Spindle and Kinetochoreassociated
(Ska) complex. The Ska complex is a key protein assembly -consisting of Ska1,
Ska2 and Ska3- essential for stabilising load-bearing end-on kinetochore-microtubule
attachments, and it is also found in the central spindle and midbody at the end of mitosis.
Our research shows that the interaction between PP2A(B55) and the Ska complex is
mediated by a short unstructured region of Ska3. This region binds the B55 subunit of PP2A
and, according to our predicted models, it might involve its substrate-binding groove.
Ongoing efforts in human cell lines aim to explain how this interaction controls the
localisation and function of the Ska complex during late mitotic events.