Model for the structure of bacteriorhodopsin based on high-resolution electron cryo-microscopy.

EMAN: semiautomated software for high-resolution single-particle reconstructions.

The structure of the light-harvesting chlorophyll a/b-protein complex, an integral membrane protein, has been determined at 3.4 A resolution by electron crystallography of two-dimensional crystals. Two of the three membrane-spanning alpha-helices are held together by ion pairs formed by charged residues that also serve as chlorophyll ligands. In the centre of the complex, chlorophyll a is in close contact with chlorophyll b for rapid energy transfer, and with two carotenoids that prevent the formation of toxic singlet oxygen.

Atomic model of plant light-harvesting complex by electron crystallography

Human red cell AQP1 is the first functionally defined member of the aquaporin family of membrane water channels. Here we describe an atomic model of AQP1 at 3.8A resolution from electron crystallographic data. Multiple highly conserved amino-acid residues stabilize the novel fold of AQP1. The aqueous pathway is lined with conserved hydrophobic residues that permit rapid water transport, whereas the water selectivity is due to a constriction of the pore diameter to about 3 A over a span of one residue. The atomic model provides a possible molecular explanation to a longstanding puzzle in physiology-how membranes can be freely permeable to water but impermeable to protons.

K. H. Downing

Papers

Structure of purple membrane from halobacterium halobium: recording, measurement and evaluation of electron micrographs at 3.5 Å resolution

A model for the structure of bacteriorhodopsin based on high resolution electron cryomicroscopy