Cell biology: Brief encounters bolster contacts

Molecules often work together in complexes to carry out their functions in the cell. But how do they get together in such a dynamic environment? A structural study follows proteins as they meet their partners.Close encountersProtein–protein interactions are involved in a large number of biological processes, and though X-ray crystallography and nuclear magnetic resonance spectroscopy can be used to examine two (or more) proteins in a complex, it is difficult to establish how the two proteins interact before they form this final complex. Tang et al. have used nuclear magnetic resonance spectroscopy to directly visualize an ensemble of transient, non-specific encounter complexes for the first binary complex in the bacterial phosphotransferase system (the N-terminal domain of enzyme I and the phosphocarrier protein HPr). Of particular interest is the observation that the distribution of encounter complexes correlates with the electrostatic surface potentials on the interacting proteins.