Authors: J. Lin and T.S.T. Tan
Affilation: National Tsing Hua Univ., Taiwan
Pages: 39 - 42
Keywords: S-layer protein, self-assembly, particle-size analysis
Proteins capable of self-assembly are crucial to many bio-architectures and have potential applications in nanotechnology. An example is the group of proteins used to construct crystalline surface layers (S-layers) in nearly all archaebacteria and many eubacteria. One extensively studied S layer is the hexagonally packed intermediate layer, which represents the major cell envelope protein of the radioresistant bacterium Deinococcus radiodurans. The cell envelop of this bacterium is unique in having both a Gram-positive-specific trait (thick peptidoglycan layer) and a Gram-negative-specific trait (outer membrane). We have found that D. radiodurans is capable of forming multi-cell-forms (Chou & Tan, J. Bacteriol. 173:3184-3190, 1991) which are made possible by producing many cross-walls and a large S-layer in a bacterial particle. We have recently isolated a novel slow-growing, desiccation-intolerant mutant that appears to have defect in construction of its S-layer (Tan, T.S.T. et al., manuscript in preparation). Here, we report our study on the self-assembly capacity of D. radiodurans S-layer proteins in vitro. Our results showed that the self-assemblies were (i) micron-scale sheet structures when observed under light microscope and electron microscopes (Figs. 1, 2), (ii) regularly patterned on their surface (Fig. 1), (iii) multi-layered structures (field-emission SEM, particle-size analysis, Fig, 3), and (iv) made of high-molecular-weight cell wall proteins (~100 kDa). In summary, we have demonstrated the in vitro assembly capability of the S-layer proteins isolated from D. radiodurans, and established a method to monitor the in vitro self-assembly process by using an electronic particle-size analyzer. These results should be useful in the application of S-layer proteins as a novel biomaterial to fabricate nano-and micro-structures.