The structure of the α-hemolysin transmembrane pore in native and divalent cation inhibited forms

Abstract

The cytochrome bel complex from bovine mitochonchia plays a central role in cell respiration. It is a membrane protein complex that consists of ten protein subunits and tom redox centers with a molecular weight of240,000 Daltons. Its crytallization has been repmted by several laboratmies. Ow· crystals, grown in the presence of glycerol, diffract Xray to better than 3 A resolution under cryogenic conditions. They have the symmel!Y of the spac;: group I4 1 22 with unit cell dime11sions of a=b=l 53 .S A and c=597. 7 A, and one bel complex in th;: crystallographic asymmetric unit. Pha<;es have been determined to 3.3 A resolution by the MIR method with fom heavy atom derivatives. The solvent flattened · electr·on density clearly shows the tr·ansmemebrane region with thirteen tr·ar1smembrane helices. Fom high peaks in the electr·on density ar1d in maps calculated using ar1omalous scattering data mea>umd near· the ir·on absorption edge ar·e ir1terpreted as the redox centers of the bel complex. Two of these sites are 20 A apart in the trar1smembrane region and most likely represent the heme ir·ons of cytochromes bs62 ar1d bs66· Another site near· the membrane smface ar1d 26 A away from the near-est b-heme could be the ir·on -sulf1.rr center~ the fomth site, presumably the cytochrome cl heme is 31 A apart from this center. The majmity of the molecular· mass outside the membrane is located on the side of the membrane opposite from the redox centers, presumably the matrix side of the mitochonchial membrar1e. The electr·on density map also reveals a very tight association of two monomers related by a two-fold symmetry. The overall dirnensions of the dimer ar-e about 130 A in diar-neter and 151 A in height, with the heights for tl1e inter-membrane space region, the tr·ansmembrane region ar1d t11e matri'\ region 41 A, 35 The reaction center of Photosystem II (Rem, a -250 kDa membrarle bound protein/pigment complex has been crystallized. RCII catalyzes the photochemically chiven transfer of electr·ons from water, resulting in tl1e fmmation of reduced and protonated quinones and the evolution of molecular-oxygen. It is tl1e somce of linear· electr·on t1ow utilized by all oxygenic photosyntl1etic organisms for botl1 the reduction ofNADP and the fom1ation of the proton gradient needed tor l\TP synt11esis. It is highly conserved in all species at all levels of str1.rct11re and function. Isolation procedmes have been developed for RCII from a variety of photosyntl1etic organisms witl1 an emphasis not only on pmity, but homogeneity and stability as well. Isolated RCII has been crystallized by the vapor diffusion method. Two Ciystal fon11s of isolated spinach RCII have been obtained: hexagonal rods and rectar1gular rods (with dir11en-sions of 0.3 x 0.3 x 1.0 mm). These Ciystals diffract to a maximum resolution of 7 A, using synchrotr·on radiation (SSRL Stanford). The crystals were however quite mosaic, appar-ently due to tl1eir sensitivity to physical str·ess. Botl1 crystal forms were obtained in tl1e presence of mixrures of two no...