Structures of membrane proteins determined at atomic resolution.
Following determination of the first crystal structure of the reaction center of Rhodopseudomonas viridis, a membrane protein, by X-ray crystal structure analysis at 3.0 A resolution, 18 X-ray crystal structures and two electron crystal structures of membrane proteins have been obtained at higher than 3.5 A resolution. Besides these integral membrane protein structures, three crystal structures of water-soluble proteins, which can enter membranes, have been determined by X-ray crystallography at high resolution. The structural features of membrane proteins have been summarized by inspecting these crystal structures. The polypeptide chain crosses the membrane in a helical conformation or a beta-strand. The central +10 A region of the transmembrane alpha-helix is dominated by hydrophobic residues. On both sides of the central region are concentrated polar aromatic residues. Charged residues are dominant around +15 A to +20 A. All the transmembrane beta-structures are found in pore-forming proteins. The central region of the transmembrane beta-structure is amphipathic with hydrophobic residues on the membrane exposed side. The distribution of amino acid residues on the membrane exposed surface of the transmembrane beta-structure is similar to that of the transmembrane alpha-helix. alpha-Helices anchoring the membrane surface region are amphipathic with hydrophobic residues inside and hydrophilic residues outside.
Sakai
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Institute for Protein Research, Osaka University, Suita, Osaka, 565-0871, Japan.
Tsukihara
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D000818:Animals; D001427:Bacterial Toxins / Q000737:chemistry; D001436:Bacteriorhodopsins / Q000737:chemistry; D002462:Cell Membrane / Q000737:chemistry; D003087:Colicins / Q000737:chemistry; D018360:Crystallography, X-Ray / Q000379:methods; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry*; D008958:Models, Molecular; D052899:Pore Forming Cytotoxic Proteins; D018272:Porins / Q000737:chemistry; D015221:Potassium Channels / Q000737:chemistry; D011487:Protein Conformation
D001427:Bacterial Toxins; D003087:Colicins; D008565:Membrane Proteins; D052899:Pore Forming Cytotoxic Proteins; D018272:Porins; D015221:Potassium Channels; D001436:Bacteriorhodopsins; C032676:aerolysin