Cover picture: Diffusion of glycerol through the homotetrameric Escherichia coli aquaporin GlpF. A cross-sectional view of one of the four channels (orange ribbons) highlights pore-lining residues (blue transparent surface) and residues Phe-200 and Arg-206 of the selectivity filter (licorice). The pore is filled with water (licorice) and contains one glycerol molecule (space-filling) located at the selectivity filter. Glycerol tumbles and isomerizes as it diffuses along the narrow channel. See the article by Hénin et al. on page 832.