Unveiling the activation dynamics of a fold-switch bacterial glycosyltransferase by 19F NMR

Abstract

Fold-switch pathways remodel the secondary structure topology of proteins in response to the cellular environment. It is a major challenge to understand the dynamics of these folding processes. Here, we conducted an in-depth analysis of the ?-helix?to??-strand and ?-strand?to??-helix transitions and domain motions displayed by the essential mannosyltransferase PimA from mycobacteria. Using(19)F NMR, we identified four functionally relevant states of PimA that coexist in dynamic equilibria on millisecond-to-second timescales in solution. We discovered that fold-switching is a slow process, on the order of seconds, whereas domain motions occur simultaneously but are substantially faster, on the order of milliseconds. Strikingly, the addition of substrate accelerated the fold-switching dynamics of PimA. We propose a model in which the fold-switching dynamics constitute a mechanism for PimA activation.