FlgM gains structure in living cells

Intrinsically disordered proteins such as FIgM play important roles in biology, but little is known about their structure in cells. We use NMR to show that FIgM gains structure inside living Escherichia coli cells and under physiologically relevant conditions in vitro, i.e., in solutions containing high concentrations (greater than or equal to400 g/liter) of glucose, BSA, or ovalbumin. Structure formation represents solute-induced changes in the equilibrium between the structured and disordered forms of FIgM. The results provide insight into how the environment of intrinsically disordered proteins could dictate their structure and, in turn, emphasize the relevance of studying proteins in living cells and in vitro under physiologically realistic conditions.