| Background |
Protein phosphatase type 2A (PP2A) is an essential protein serine/threonine phosphatase that is conserved in all eukaryotes. PP2A is a key enzyme within various signal transduction pathways as it regulates fundamental cellular activities such as DNA replication, transcription, translation, metabolism, cell cycle progression, cell division, apoptosis and development Active protein phosphatase 2A is composed of both structural (A) and catalytic (C) proteins, and its activity relies on interaction with regulatory (B) subunits. An important PP2A regulatory subunit is PP2A phosphatase activator (PTPA), also known as the PP2A activator regulatory subunit 4 (PPP2R4) This PTPA regulatory protein binds ATP and has isomerase (PPIase) activity, suggesting that PP2A regulation involves a change in phosphatase conformation. The addition of ATP (and Mg2+) results in a correlated increase in both PP2A activation and PTPA isomerase activity While the exact mechanism is still under consideration, evidence suggests that binding of PTPA to the PP2A A-C dimer produces a conformational change in PP2A that shifts phosphatase substrate specificity from phosphoserine to phosphotyrosine substrates.
|