Effects of Mutations on Tandem-Repeat Proteins Conformation Mechanisms. Application to the Phosphatase PP2A

Tandem repeat proteins (TRPs) are composed of arrays of repeating structural units that assemble into extended, superhelical, or horseshoe-shaped architectures stabilized primarily by short-range interactions. The unique sequence-structure-dynamics-function relationships of TRPs have been the subject of extensive investigation, aiming to elucidate the molecular principles that distinguish them from globular proteins. Here we explore the effects of mutations on conformational mechanics of PR65, the HEAT-repeat scaffold of phosphatase PP2A that acts as an elastic connector between catalytic and regulatory subunits. We found that the effect of mutations on dynamics, that is associated with the collective conformational changes experienced by PR65 in its binding to the catalytic subunit, correlates with its evolutionary conservation. Besides, our study reveals a common pattern among repeat units in how mutations influence these dynamics, but it also highlights functional differences among the individual units. That is, mutations on individual units preserve a common influence on the collective dynamics of the TRP but their individual participation in function introduces additional differences in their corresponding effects of mutations. Finally, none of these aspects are observed for the subsequent conformational changes experienced during the binding of the dimer PR65-catalytic subunit complex with the regulatory subunit. We believe this work highlights both the similarities and differences between repeat units in how mutations affect their dynamics─insights that may advance our understanding of TRP mechanisms in pathogenicity─enable scaffold modifications for engineered ligand binding with diverse applications, and broadly expand our knowledge of TRP function.