10 September 2004
Vol 305, Issue 5690

About The Cover

Cover image expansion

COVER Crystallographic structure of AmtB, a bacterial channel that transports the gas ammonia. During transport, ammonium ions (NH4+, the green sphere) are recruited and -cation stabilized; then only uncharged ammonia (NH3) enters the hydrophobic channel itself (three purple spheres). This mechanism prevents leakage of other ions or transmembrane potential. See page 1587. [Image: S. Khademi]