# Structural Basis for Small Molecule-Mediated Allosteric Activation of Protein Phosphatase 2A

> **NIH NIH K99** · DANA-FARBER CANCER INST · 2021 · $136,080

## Abstract

The group of phosphatases collectively referred to as PP2A (protein phosphatase 2A) represent an 
important family of tumor suppressors. As a research fellow working under the mentorship 
of Dr. Thomas Look, the candidate has recently discovered that perphenazine (PPZ), a classic 
antipsychotic drug, and its related small molecule iHAP1 selectively drive the formation of 
heterotrimeric PP2A complexes containing the B56ϵ (PPP2R5E) subunit out of 15 possible 
distinct regulatory B subunits (K. Morita et al. Cell. 2020). Defining the structural mechanisms 
through which these small molecules allosterically activate PP2A with extreme specificity is of 
paramount importance because such knowledge will fundamentally advance the field of phosphatase 
biology, while forming the basis for medicinal chemists to optimize these tool compounds as novel 
anticancer therapeutics for clinical study. In this grant proposal, the candidate seeks 
to understand the fundamental mechanisms responsible for this allosteric activation of PP2A 
phosphatase from a structural perspective, working under the primary mentorship of Dr. Eric 
Fischer, an emerging leader in biochemistry and the field of structural biology. The central 
hypothesis is that PPZ/iHAP1 binds to the AC heterodimer and allosterically alters its conformation 
-- in ways that will be evident from the high-resolution crystal structure -- so that the B56ϵ
subunit is readily recruited, thus driving the formation and activation of the PP2A-B56ϵ
phosphatase in the cell. The immediate objectives are to determine the three-dimensional 
protein structures of the PP2A holoenzyme complexes formed in response to PPZ/iHAP, and to 
define the molecular contacts of the PP2A subunits with PPZ/iHAP compounds by X-ray 
crystallography. This goal will be pursued in two specific aims: 1) Determine the three-dimensional 
structure of the PP2A holoenzyme complex in the presence of PPZ or iHAP compounds to decipher the 
mechanisms underlying allosteric activation of specific PP2A subunit complexes by these small 
molecules, and 2) Determine the biochemical mechanisms underlying the ability of allosteric 
small-molecule PP2A activators to drive dynamic exchange of the PP2A regulatory B subunits with the 
AC heterodimer, from the Striatin family proteins in control cells to the B56ϵ or B55α proteins for 
iHAP/PPZ and SMAP, respectively. This strategy is significant because the results could reveal new 
mechanisms underlying allosteric activation of specific PP2A phosphatase complexes, which in turn 
will be key to dissecting the normal physiologic roles of this diverse family of phosphatases and 
to understanding their roles as tumor suppressors and how they are subverted in malignant 
transformation. This proposal has been designed to provide the candidate with advanced training in 
structural biology, as well as mentoring in manuscript/grant writing and leadership qualities. 
Bolstered by the guidance of a new primary mentor,...

## Key facts

- **NIH application ID:** 10191568
- **Project number:** 1K99CA259530-01
- **Recipient organization:** DANA-FARBER CANCER INST
- **Principal Investigator:** Ken Morita
- **Activity code:** K99 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $136,080
- **Award type:** 1
- **Project period:** 2021-05-03 → 2021-07-15

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10191568

## Citation

> US National Institutes of Health, RePORTER application 10191568, Structural Basis for Small Molecule-Mediated Allosteric Activation of Protein Phosphatase 2A (1K99CA259530-01). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10191568. Licensed CC0.

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