Targeting PP1: NMR takes aim

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  • Published: Mar 15, 2014
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Targeting PP1: NMR takes aim

Risky targets

The enzyme PP1, the tan-coloured mass above, is everywhere in the body and has a role in nearly every biological process. That role is shaped more than 200 regulatory proteins that bind to PP1, including one called PNUTS, blue and pink above.	 Credit: Page lab/Brown University

The enzyme PP1, protein phosphatase 1, plays a vital role in countless biochemical processes in the body and is the pivot around which many diseases, including various cancers, turn. It is so ubiquitous that until now drug development has tended to avoid it because the side effects and complications that arise when it is targeted are too risky. Now, researchers at Brown University, have used NMR spectroscopy and X-ray crystallography to help them focus on how PP1 interacts with other proteins to understand specific behaviour that might nevertheless be targeted for precise benefits.

The primary role of PP1 is to facilitate the transmission of molecular messages between cells in the body and as such it is found throughout our tissues. As such, it has a vast roster of responsibilities involved in the healthy functioning of our bodies and it is apparent in many diseases states in which it goes awry. Brown's Rebecca Page points out that the diversity of its functions in the body has precluded it as a target for the development of pharmaceutical interventions in disease. If it is over-stimulated or conversely inhibited that can trigger a cascade of unwanted effects even if the initial aim of controlling it in a particular disease is reached.

Can touch this

"The amazing thing about PP1 is that no one has wanted to touch it for the most part as a drug target because PP1 is involved in nearly every biological process," Page explains. "It’s not like you could just target the PP1 active site for, let's say, diabetes because then you are going to affect drug addiction, Alzheimer’s disease and all these other diseases at the same time." In other words, a PP1 inhibitor in one context will affect other areas of the body. As such, structural biologist Page and her co-author Wolfgang Peti are keen to determine what contexts gives rise to specific behaviour of PP1 in particular settings around the body in health and disease.

The key to understanding PP1 is knowing that it binds to more than 200 different regulatory proteins and the determination of the structures of these proteins and their interactions with PP1. "The ability to predict how these PP1-interacting proteins bind the enzyme from [amino acid] sequence alone is still missing," Page laments. Now, Page, Peti and their colleagues Meng Choy, Martina Hieke, Ganesan Senthil Kumar, Greyson Lewis, Kristofer Gonzalez-DeWhitt, Rene Kessler, Benjamin Stein, and Manuel Hessenberger of Brown and Yale University's Angus Nairn have combined nuclear magnetic resonance spectroscopy, X-ray crystallography and various biochemical techniques to reveal the PP1 binding motifs when the target protein is PNUTS - protein phosphatase 1 nuclear targeting subunit. The information gleaned from this study has been combined with earlier research into two other targeting proteins - NIPP1 (nuclear inhibitor of protein phosphatase-1) and spinophilin -which has allowed the researchers to predict how PP1 binds with some 43 of those 200 regulatory proteins that give rise to its specific behaviour.

Motifs and conjunctions

"What this work in conjunction with two of our previous structures allowed us to do was to define two entirely new binding motifs," Page explains. "From that, comparing the sequences with the known proteins that interact with PP1 whose structures we don't have, we were able to predict that 20 percent of them likely interact in a way that is similar to these three proteins." Thus by gain the structures of just three proteins bound to PP1, the team now has the necessary insights to work out the interaction based on the binding motifs and on the known amino acid sequences of other proteins without having to determine their precise molecular structures, which are often off-limits to crystallography.

As for PP1's interactions with the other 80 percent or so of regulatory proteins, those remain a mystery. But Page said the success her team has had in the lab working with PP1 and resolving key motifs makes her optimistic that those interactions can be solved, too.

Related Links

Proc Natl Acad Sci, 2014, online: "Understanding the antagonism of retinoblastoma protein dephosphorylation by PNUTS provides insights into the PP1 regulatory code"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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