We have described recently the purification and cloning of PP2A (protein phosphatase 2A) leucine carboxylmethyltransferase. We studied the purification of a PP2A-specific methylesterase that co-purifies with PP2A and found that it is tightly associated with an inactive dimeric or trimeric form of PP2A. These inactive enzyme forms could be reactivated as Ser/Thr phosphatase by PTPA (phosphotyrosyl phosphatase activator of PP2A). PTPA was described previously by our group as a protein that stimulates the in vitro phosphotyrosyl phosphatase activity of PP2A; however, PP2A-specific methyltransferase could not bring about the activation. The PTPA activation could be distinguished from the Mn2+ stimulation observed with some inactive forms of PP2A, also found associated with PME-1 (phosphatase methylesterase 1). We discuss a potential new function for PME-1 as an enzyme that stabilizes an inactivated pool of PP2A.
- phosphotyrosyl phosphatase activator
- protein phosphatase 2A (PP2A)
- signal transduction
Abbreviations used: AdoMet, S-adenosylmethionine; DTT, dithiothreitol; EST, expressed sequence tag; LCMT, leucine carboxylmethyltransferase; PME-1, phosphatase methylesterase 1; pNPP, p-nitrophenyl phosphate; PP2A, protein phosphatase 2A; PP2Ai, inactive form of PP2A; PTPA, phosphotyrosyl phosphatase activator of PP2A (or phosphatase two A phosphatase activator).
- The Biochemical Society, London ©2004