A S‐Layer Protein of Bacillus anthracis as a Building Block for Functional Protein Arrays by In Vitro Self‐Assembly

S‐layer proteins create a cell‐surface layer architecture in both bacteria and archaea. Because S‐layer proteins self‐assemble into a native‐like S‐layer crystalline structure in vitro, they are attractive building blocks in nanotechnology. Here, the potential use of the S‐layer protein EA1 from Bacillus anthracis in constructing a functional nanostructure is investigated, and apply this nanostructure in a proof‐of‐principle study for serological diagnosis of anthrax. EA1 is genetically fused with methyl parathion hydrolase (MPH), to degrade methyl parathion and provide a label for signal amplification. EA1 not only serves as a nanocarrier, but also as a specific antigen to capture anthrax‐specific antibodies. As results, purified EA1–MPH forms a single layer of crystalline nanostructure through self‐assembly. Our chimeric nanocatalyst greatly improves enzymatic stability of MPH. When applied to the detection of anthrax‐specific antibodies in serum samples, the detection of our EA1–MPH nanostructure is nearly 300 times more sensitive than that of the unassembled complex. Together, it is shown that it is possible to build a functional and highly sensitive nanosensor based on S‐layer protein. In conclusion, our present study should serve as a model for the development of other multifunctional nanomaterials using S‐layer proteins.