Figure 1

Structure of protein phosphatase 2A holoenzymes. A is the structural subunit and scaffolding protein, and C is the catalytic subunit. B/B’/B”/B”’ are the variable and regulatory subunits. PP2A predominantly exists in cells as a heterotrimetic holoenzyme, which consists of a 36 kDa catalytic subunit (PP2A-C), a 65kDa structural subunit (PP2A-A) forming a core enzyme, and a variable regulatory subunit (PP2A-B). The A structure subunit recruits the C catalytic subunit to form the core dimer, which acts as a scaffold for the C and B subunits of the enzyme. Four B subunit families including PR55or B, PR61 or B’, PR72/130 or B” and PR93/PR110 or B”’ interact via the same or overlapping sites within the A subunit of the core dimer. The PP2A holoenzyme's substrate specificity, enzymatic activity, and/or cellular localization can be modulated by the B regulatory subunit.