Self-assembled lipid and membrane protein polyhedral nanoparticles.

We demonstrate that membrane proteins and phospholipids can self-assemble into polyhedral arrangements suitable for structural analysis. Using the Escherichia coli mechanosensitive channel of small conductance (MscS) as a model protein, we prepared membrane protein polyhedral nanoparticles (MPPNs) with uniform radii of ∼ 20 nm. Electron cryotomographic analysis established that these MPPNs contain 24 MscS heptamers related by octahedral symmetry. Subsequent single-particle electron cryomicroscopy yielded a reconstruction at ∼ 1-nm resolution, revealing a conformation closely resembling the nonconducting state. The generality of this approach has been addressed by the successful preparation of MPPNs for two unrelated proteins, the mechanosensitive channel of large conductance and the connexon Cx26, using a recently devised microfluidics-based free interface diffusion system. MPPNs provide not only a starting point for the structural analysis of membrane proteins in a phospholipid environment, but their closed surfaces should facilitate studies in the presence of physiological transmembrane gradients, in addition to potential applications as drug delivery carriers or as templates for inorganic nanoparticle formation.

Effects of two surface finishes on the color of cemented and colored anatomic-contour zirconia crowns.

STATEMENT OF PROBLEM: The esthetic appearance of anatomic-contour zirconia restorations is influenced by the shade of the coloring liquid and the optical properties of the luting cements. However, few studies are available on the effects of surface-finishing methods and luting cements on colored anatomic-contour zirconia restorations. PURPOSE: The purpose of this in vitro study was to investigate the effects of surface finishing methods on the color distribution of colored anatomic-contour zirconia crowns before and after being cemented onto abutments. MATERIAL AND METHODS: Implant-supported anatomic-contour zirconia premolar crowns were fabricated and immersed in A3-coloring liquid for 30 seconds. The colored zirconia crowns were separated into 3 groups according to the method of surface treatment: no treatment (N), polishing (P), and glazing (G). The zirconia crowns without coloring liquid application served as the control group. CIELab color coordinates were obtained, and color differences (ΔE) between shaded crowns were calculated with a spectrophotometer. The color stability of the crown before and after cement application was also investigated. RESULTS: Before cement application, the mean color difference between groups N and P was 2.85 ΔE units, whereas the mean ΔE value between groups N and G was 3.27. Mean ΔE values with and without cement application among groups ranged from 2.75 to 3.45 ΔE units. CONCLUSIONS: The color appearance of the colored zirconia crowns was strongly influenced by the surface-finishing methods and luting cement application.