Conformational change of the hexagonally packed intermediate layer of Deinococcus radiodurans monitored by atomic force microscopy

Both surfaces of the hexagonally packed intermediate (HPI) layer of Deinococcus radiodurans were imaged in buffer solution by atomic force microscopy. When adsorbed to freshly cleaved mica, the hydrophilic outer surface of the HPI layer was attached to the substrate and the hydrophobic inner surface was exposed to the stylus. The height of a single HPI layer was 7.0 nm, while overlapping edges of adjacent single layers adsorbed to mica had a height of 14.7 nm. However, double-layered stacks with inner surfaces facing each other exhibited a height of 17.4 nm. These stacks exposed the outer surface to the stylus. The different heights of overlapping layers and stacks are attributed to differences in the interaction between inner and outer surfaces. At high resolution, the inner surface revealed a protruding core with a central pore connected by six emanating arms. The pores exhibited two conformations, one with and the other without a central plug. Individual pores were observed to switch from one state to the other. Nearly all archaebacterial cell envelopes incorporate a reg-ular surface layer (S layer) of protein or glycoprotein subunits (17). S layers are also widely distributed among eubacteria but less ubiquitously than among archaebacteria (3, 25). Electron microscopy has served as the major tool to elucidate thei