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			== Protein phosphatase 2 ==
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'''Protein phosphatase 2''' (PP2), also known as '''PP2A''', is a major serine/threonine-specific [[protein phosphatase]] that plays a critical role in cellular regulation. It is involved in various cellular processes including cell growth, division, and death. PP2A is a holoenzyme that consists of a structural A subunit, a regulatory B subunit, and a catalytic C subunit. This enzyme is highly conserved across eukaryotic species, underscoring its importance in cellular physiology.

==Structure==
PP2A is a trimeric holoenzyme. The core enzyme comprises the A and C subunits, where the A subunit serves as a scaffolding molecule, binding both the C subunit and one of the several regulatory B subunits. The C subunit is the catalytic moiety of the enzyme. The B subunit determines the substrate specificity, cellular localization, and the regulatory properties of the holoenzyme. There are multiple isoforms of each subunit (Aα/β, B family members, and Cα/β), which allow for a diversity of PP2A complexes, each targeting different substrates and functions.

==Function==
PP2A is involved in the negative regulation of cell growth and division. It dephosphorylates a variety of key cellular proteins, including those involved in the signaling pathways for cell growth and apoptosis. For example, it can dephosphorylate the [[cyclin-dependent kinase]]s (CDKs), which are critical for cell cycle progression. By dephosphorylating these kinases, PP2A acts as a tumor suppressor, inhibiting the uncontrolled growth of cells.

In addition to its role in cell cycle regulation, PP2A also participates in the regulation of DNA replication and repair, [[apoptosis]], and protein synthesis. It is involved in the control of [[MAP kinase]] signaling pathways, which are important for cell response to growth factors and stress.

==Regulation==
The activity and specificity of PP2A are regulated by the interaction of the core enzyme with its regulatory B subunits, as well as by post-translational modifications of its subunits, such as methylation and phosphorylation. The methylation of the C subunit, for example, is essential for the binding of certain B subunits, affecting the substrate specificity and localization of the holoenzyme.

==Clinical Significance==
Alterations in the expression or activity of PP2A have been implicated in the development of several diseases, including cancer. Overexpression or mutations in the B subunits can lead to aberrant PP2A activity, contributing to tumorigenesis. Conversely, restoration of PP2A activity has been proposed as a therapeutic strategy in certain cancers.

PP2A also plays a role in neurodegenerative diseases. It is involved in the dephosphorylation of tau protein, and its dysfunction has been linked to [[Alzheimer's disease]] and other tauopathies.

==Research Directions==
Current research is focused on understanding the complex regulation of PP2A, identifying its various substrates, and exploring its role in diseases. There is also significant interest in developing PP2A as a therapeutic target, particularly in cancer and neurodegenerative diseases.

[[Category:Enzymes]]
[[Category:Cell biology]]
[[Category:Molecular biology]]
{{Medicine-stub}}

Protein phosphatase 2 - Revision history

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