In most archaebacteria, a protein coat is the primary structure that surrounds and shapes the cell. This coat of protein armor is composed of a paracrystalline array of “surface layer proteins.”
Half a million surface layer proteins line next to each other to form a shell that encloses the cell. Inside the shell, they bind to sugar chains on the cell surface, or in the case of archaebacteria, interact directly with the membrane. This protein coat provides protection, and it can also assist in the gathering of nutrients and attachment to targets in the environment.
- Kern, J. et al. Structure of surface layer homology (SLH) domains from Bacillus anthracis surface array protein. J. Biol. Chem. 286, 26041-26049 (2011)