title: Three-dimensional structure of the tetragonal surface layer of Sporosarcina ureae.
abstract: The three-dimensional structure of the regular surface layer of Sporosarcina ureae has been determined to a resolution of 1.7 nm by electron microscopy and image reconstruction. The S-layer has p4 symmetry, a lattice constant of 12.9 nm, and a minimum thickness of 6.6 nm. The reconstruction reveals a distinct domain structure: a massive core, arms connecting adjacent unit cells, and spurs which make contact at the subsidiary fourfold symmetry axes. In the z-direction the domains appear to be arranged in three planes, creating two entirely different surface reliefs. The S-layer has a complex pattern of pores and gaps that are 2 to 3 nm wide. In addition, the secondary-structure composition has been determined by infrared spectroscopy: about 35% of the polypeptide appears to have a beta-structure conformation.
mesh_terms: D001426:Bacterial Proteins; D006094:Gram-Positive Bacteria / Q000648:ultrastructure*; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D011487:Protein Conformation; D013055:Spectrophotometry, Infrared
chemical_list: D001426:Bacterial Proteins