Single-particle study of protein assembly - art. no. 041911

A study of protein assembly in solution with single-particle imaging and re construction techniques using cryoelectron microscopy is reported. The huma n glutamine synthetase enzyme, important in brain metabolism, and previousl y assumed to be assembled into a homogeneous quaternary structure, is found to be heterogeneous, with three oligomeric states that co-exist at room te mperature. This result corrects an old structural and kinetic model determi ned by ensemble averaging techniques that assumed a homogeneous system. Une xpectedly fast protein dissociation kinetics results from a stabilized tran sition state.