Three-dimensional structure of luminal plasma membrane protein from urinary bladder.

The structure of the membrane protein from urothelial plasma membrane has been investigated. A three-dimensional map has been obtained at 35 A resolution from negatively stained two-dimensional arrays of membrane proteins. The lattice space group has the symmetry p6. Twelve stain-excluding areas are resolvable on projections perpendicular to the membrane plane. In the three-dimensional reconstruction these areas appear to be restricted to one side of the membrane and form protrusions that extend 50 A out of the membrane. No periodic structure is observed at the cytoplasmic side of the membrane, which suggests that the protein is not a transmembrane protein.