Three-D structure of luminal plasma membrane protein from urinary bladder
We present a low resolution (35 Å) three dimensional reconstruction of the molecular form of the membrane protein which forms the naturally occuring crystalline arrays of the luminal plasma membrane of the mammalian urinary bladder.This membrane consists of concave plaques 120 Å thick with 80 Å thick interplaque regions, giving the scalloped appearance observed on thin sections. Isolated luminal membranes, observed by negative staining and freeze etching present reqular hexagonal arrays of particles with a lattice parameter of 160 Å. Image averaging techniques show that the particles possess 6 or 12 resolvable subunits having a stellate appearance. These arrays called hexagonal membranes correspond to the 120 Å thick concave plaques. Thin sections show the hexagonal membrane to be asymmetric,with a 80 Å thick luminal leaflet and a 40 Å thick cytoplasmic leaflet.The isolation procedure described by Caruthers and Bonneville was followed with slight modifications. 1 % PTA (pH 7.0-7.4) was used as negative stain.