Cover picture: Outer membrane transport in action. The outer membrane vitamin B12 transporter BtuB (blue) is shown in complex with part of the energy-transmitting protein TonB (red), which connects the energy-generating inner membrane and the passive outer membrane. Simulation of the proteins in their native water and lipid environment was used to investigate a force-activated mechanism for transport across the outer membrane. See the article by Gumbart et al. on page 496.