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Scripps Research Institute
New research shows how NPM1—a protein implicated in non-Hodgkin lymphoma, acute myelogenous leukemia, and other cancers—twists and morphs into different structures.
This protein has many functions and, when mutated, has been shown to interfere with cells’ normal tumor suppressing ability.
Previous research showed that a section of NPM1, called the N-terminal domain, doesn’t have a defined, folded structure.
Instead, the protein morphs between 2 forms: a 1-subunit disordered monomer and a 5-subunit folded pentamer.
Until now, the mechanism behind this transformation was unknown, but researchers believed this monomer-pentamer equilibrium could be important for the protein’s location and functioning in the cell.
Ashok Deniz, PhD, of The Scripps Research Institute in La Jolla, California, and his colleagues conducted the current study to shed light on how this transformation occurs. They reported their findings in Angewandte Chemie.
The researchers used a combination of 3 techniques to analyze NPM1—single-molecule biophysics, fluorescence resonance energy transfer, and circular dichroism.
These techniques revealed that NPM1’s transformation can proceed through more than one pathway. In one pathway, the transformation begins when the cell sends signals to attach phosphoryl groups to NPM1.
This phosphorylation prompts the ordered pentamer to become disordered and likely causes NPM1 to shuttle outside the cell’s nucleus. A meeting with a binding partner can mediate the reverse transformation to a pentamer.
However, when NPM1 does become a pentamer again under these conditions, which likely causes it to move back to the nucleolus, it takes a different path instead of just retracing its earlier steps.
The study also revealed many intermediate states between monomer and pentamer structures. And it showed that these states can be manipulated or “tuned” by changing conditions such as salt levels, phosphorylation, and partner binding, which may explain how cells regulate NPM1’s multiple functions.
The researchers said future studies could shed more light on the biological functions of these different structures and how they might be used in future cancer therapies.
“We’re studying basic biophysics, but we believe the complexity and rules we uncover for the physics of protein disorder and folding could one day also be used for better designs of therapeutics,” Dr Deniz said.
He and his colleagues also believe that combining the 3 techniques used in this study, plus a novel protein-labeling technique for single-molecule fluorescence, could be a useful strategy for studying other unstructured, intrinsically disordered proteins.
