Assembly status transition offers an avenue for allosteric activity modulation of a supramolecular enzyme

Abstract

Nature has evolved many supramolecular proteins assembled in certain, sometimes even seemingly oversophisticated, morphological manners. The rationale behind such evolutionary efforts is often poorly understood. Here we provide atomic-resolution insights into how the dynamic building of a structurally complex enzyme with higher-order symmetry offers amenability to intricate allosteric regulation. We have established the functional coupling between enzymatic activity and protein morphological states of glutamine synthetase (GS), an old multi-subunit enzyme essential for cellular nitrogen metabolism. Cryo-EM structure determination of GS in both the catalytically active and inactive assembly states allows us to reveal an unanticipated self-assembly-induced dynamics-driven allosteric paradigm, in which the remote interactions between two subcomplex entities significantly rigidify the otherwise structurally fluctuating active sites, thereby regulating activity. We further show in vivo evidences that how the enzyme morphology transitions could be modulated by cellular factors on demand. Collectively, our data present an example of how assembly status transition offers an avenue for allosteric modulation, and sharpens our mechanistic understanding of allostery, dynamics, cooperativity, and other complex functional and regulatory properties of supramolecular enzymes.