tailieunhanh - Nanotechnology Science and Computation Part 12

Tham khảo tài liệu 'nanotechnology science and computation part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Bacterial Surface Layer Proteins 279 oblique square pl p2 p4 Symmetry axis I Two-fold Four-fold Three-fold 0 Six-fold Fig. 2. Schematic drawings of possible S-layer lattice types. Owing to the chirality of proteins space group symmetries with mirror-reflection lines or glide-reflection lines are not possible in S-layer lattices. often lattice faults are sites for the incorporation of new morphological units and initiation points in the cell division process 53 58 . For example the S-layer of the lobed archaeon Methanocorpusculum sinense shows hexagonal lattice symmetry with numerous lattice faults pentagons and heptagons 27 . Complementary pairs of pentagons and heptagons in the hexagonal S-layer are termination points of edge dislocations and function most probably as initiation points in the cell division process 20 . Bacterial S-layer lattices are generally 5 to 20 nm thick whereas the Slayers of archaea have thicknesses up to 70 nm for reviews see 2 11 . S-layers generally represent highly porous protein meshworks 30 -70 porosity with pores of uniform size in the 2-8 nm range and of uniform morphology. High-resolution electron and scanning force microscope studies partially in combination with digital image processing have revealed a smooth topography for the outer face of most S-layers and a more corrugated topography for the inner face for reviews see 2 11 . Concerning the physicochemical properties of S-layers in Bacillacaea it has been demonstrated that the outer face is usually charge-neutral while the inner face is often net negatively charged 56 57 . The surface charge depends on a balance of exposed carboxylic acid and amine groups or an excess of one or the other. The functional groups in the S-layer lattice are aligned in well-defined positions and orientations which is a key condition for binding molecules and nanoparticles into ordered arrays on these protein lattices 34 . 280 D. Pum M. Sara B. Schuster . Sleytr 4 Secondary Cell Wall Polymers .