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The split protein phosphatase system
1MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, U.K. aberto@mrc-lmb.cam.ac.uk.
The Biochemical Journal
|December 8, 2018
Summary
Protein Phosphatase 1 (PP1) enzymes, crucial for cellular processes, achieve selectivity through a split system. This involves a catalytic subunit and a non-catalytic substrate receptor subunit working together.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Reversible protein phosphorylation regulates cellular functions via kinases and phosphatases.
- Protein kinases are well-studied, while protein phosphatases remain relatively neglected.
- Protein Phosphatase 1 (PP1) dephosphorylates many phospho-serines and phospho-threonines, controlling diverse cellular processes.
Purpose of the Study:
- To review the discovery and evolving understanding of protein phosphatases.
- To highlight the exquisite selectivity of PP1 phosphatases, challenging previous views of unselectivity.
- To propose a model for PP1 selectivity based on the interaction of catalytic and non-catalytic subunits.
Main Methods:
- Review of existing literature on protein phosphatases.
- In-depth analysis of two specific holophosphatases.
- Conceptual model development based on experimental findings.
Main Results:
- PP1 phosphatases are obligatory heteromers, unlike kinases.
- Selectivity arises from the assembly of catalytic and non-catalytic subunits, the latter acting as a substrate receptor.
- PP1 and its substrate receptors form a 'split protein phosphatase system'.
Conclusions:
- The non-catalytic subunit is essential for PP1 holoenzyme function and substrate specificity.
- The 'split enzyme' model explains how PP1 achieves selective dephosphorylation.
- This framework may aid in studying poorly understood phosphatases and identifying their substrates.
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