Structure of the Protein Phosphatase 2A Holoenzyme
[PP2AA_HUMAN] PP2A is the major phosphatase for microtubule-associated proteins (MAPs). PP2A can modulate the activity of phosphorylase B kinase casein kinase 2, mitogen-stimulated S6 kinase, and MAP-2 kinase. Cooperates with SGOL2 to protect centromeric cohesin from separase-mediated cleavage in oocytes specifically during meiosis I (By similarity). Can dephosphorylate SV40 large T antigen and p53/TP53. Activates RAF1 by dephosphorylating it at 'Ser-259'.   [2A5G_HUMAN] The B regulatory subunit might modulate substrate selectivity and catalytic activity, and also might direct the localization of the catalytic enzyme to a particular subcellular compartment. The PP2A-PPP2R5C holoenzyme may specifically dephosphorylate and activate TP53 and play a role in DNA damage-induced inhibition of cell proliferation. PP2A-PPP2R5C may also regulate the ERK signaling pathway through ERK dephosphorylation. 
Publication Abstract from PubMed
Protein Phosphatase 2A (PP2A) plays an essential role in many aspects of cellular physiology. The PP2A holoenzyme consists of a heterodimeric core enzyme, which comprises a scaffolding subunit and a catalytic subunit, and a variable regulatory subunit. Here we report the crystal structure of the heterotrimeric PP2A holoenzyme involving the regulatory subunit B'/B56/PR61. Surprisingly, the B'/PR61 subunit has a HEAT-like (huntingtin-elongation-A subunit-TOR-like) repeat structure, similar to that of the scaffolding subunit. The regulatory B'/B56/PR61 subunit simultaneously interacts with the catalytic subunit as well as the conserved ridge of the scaffolding subunit. The carboxyterminus of the catalytic subunit recognizes a surface groove at the interface between the B'/B56/PR61 subunit and the scaffolding subunit. Compared to the scaffolding subunit in the PP2A core enzyme, formation of the holoenzyme forces the scaffolding subunit to undergo pronounced conformational rearrangements. This structure reveals significant ramifications for understanding the function and regulation of PP2A.
Structure of the protein phosphatase 2A holoenzyme.,Xu Y, Xing Y, Chen Y, Chao Y, Lin Z, Fan E, Yu JW, Strack S, Jeffrey PD, Shi Y Cell. 2006 Dec 15;127(6):1239-51. PMID:17174897
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